# PWM - What is it, How does it work and how to detect it.



## Cataract

PWM is very often misunderstood or simply an unknown thing for most newbies and some older CPFers and I would like to offer the simplest explanation of what it is, how to detect it and why it is not such a good thing after all. I will do my best to avoid advanced explanations of what is the difference between voltage and current, as there are plenty of resources to learn about that, and it is definitely not a pre-requisite to understand what I’m about to reveal. 


FIRST OFF : The basics of lighting a L.E.D. 

-L.E.D stands for Light Emitting Diode. A diode is a basic component of electronics that will allow current to flow in only one direction: form positive pole (or lead) to the negative pole of your battery. 

-LED’s need a specific voltage to work properly. Originally, LED’s could only give off a fixed amount of light because the circuits controlling them would only give a fixed amount of volts, which translated in a fixed amount of current.

-There are two ways to control –that is lessen- a LED’s light output: limit the current going through the LED with sophisticated circuitry, or use PWM. Current limitation is a lot more complex and more expensive mostly because the circuit has to be designed according to the specific LED’s characteristics, in accord with the type of battery being used. 


PWM for Dummies

-PWM stands for Pulse Width Modulation. 

-Rather than limiting or controlling the voltage or current going through your LED, the voltage is fixed. When the full DC (Direct Current) voltage is sent through the LED, it will emit the maximum of light it can (basically the same as connecting directly to a fully charged battery)

-In order to allow for lower modes, this current will be transformed in a high frequency current that can allow for less total “potential” (read current) to be sent through the LED. Let’s use graphics:

Direct Current (basically, the constant voltage a normal battery will give off. I ignore the normal discharge curve for this example and let’s imagine our battery has unlimited charge):







With such an input, it is obvious that our LED will emit a fixed amount of light. Now, if we introduce PWM:






As you can see, we have now changed our constant voltage input for a square wave. In this graphic, our voltage is on half the time and off half the time. The technical term here would be that we have a 50% duty cycle (50% of the time on.) With such an input on our LED, the amount of light given off appears diminished by 50%. The reason I say it appears, is because it gives off its maximum amount of light, but only 50% of the time, so our eyes perceive only half the amount of light (more on this in the next section).

I we wanted an even lower perceived light output, let’s say 25% of the maximum, we would use a PWM input that would look like this:





(Disclaimer: I’m stuck using Paint to draw these graphics, so it might not be 100% up to scale)

In this graphic, you can see that the voltage is on only 25% of the time, in technical terms we have a 25% duty cycle, but the voltage is still switched _on_ at the same intervals as in the previous graphic. This basically means that we have a fixed frequency (number of times we switch the power on and off per second). 

So, Pulse Width Modulation simply means that we control our light with pulses and we vary (modulate) the width of these pulses to control the amount of perceived light to less than the maximum amount the LED can give off.

How Come I _Perceive_ Less Light And No Blinking Or Strobing??

Your eyes are a little like tiny cameras that take about 24 pictures per second. Your brain takes those images and assembles them into what we perceive as the continuous movie of our lives. If the PWM frequency was less than 24 times per second (or only slightly more), we would perceive it as a strobe, but if the light from a PWM controlled LED is switched fast enough – way more than 24 times per second – our eyes will perceive it as continuous... but there’s an IF here:
Let’s see through graphics what would be the main difference between a lower frequency and higher frequency PWM

LOWER FREQUENCY PWM:







HIGHER FREQUENCY PWM:







In both these graphics, the power is on half the time (50% duty cycle), but in the second graphic, the power is switched more often. 

HOW DO I PERCEIVE PWM CONTROLLED LIGHTS??? HOW DOES IT AFFECT ME???

The lower frequency PWM will be more perceivable to the eyes as a fast strobe effect – remember what it looks like to dance in a club when the only lighting around are strobes? Well, imagine that strobe is even faster, to the point that motion is almost continuous... 

With any frequency of PWM, if you sit still and stare at a fixed spot on the white wall across from you while pointing your favourite PWM controlled flashlight at it, you will never know the difference. With a PWM frequency that is too low for your perception (and this frequency is very likely to vary from one person to the next) you will definitely perceive a form of strobe effect; if you wave your hand fast enough in front of the light, it might look something like this:






Count how many thumbs I appear to have. Try waving your hand in front of your camera with normal lighting and I promise you will not see repeated edges like on this photograph.

This effect can be seen with anything that moves in relation to your eyes, but that movement has to be fast enough in relation to the PWM frequency and your own perception for you to be able to perceive it. Some people see it more, some people see it less. 

If you find out your favourite reading light has bad PWM effect when waving your hand in front of it, but never use it for anything else, it might still be very useful to you. If, on the other hand, whenever you read by flashlight you get a headache, it might be worth trying another light just to see if there is any relation. I know PWM can affect me in some ways and I’ll get to that later (of course, it doesn’t mean everyone is affected, but some applications are definitely more critical than others)


How Can I Detect PWM On Higher Frequency Lights?

AAhhhh.... I only ask this question because I found a very nice answer to this one that doesn’t involve taking your light apart or expensive electronic equipment. Waving your hand in front of, let’s say a Quark Mini, will not show any signs of PWM... but the Mini’s ARE PWM controlled! The frequency used is simply high enough that you will not (or not likely) perceive it when using the light. So how was I able to tell that without even opening it up?

This kinda brings me to a very old stupid joke that I will botch on purpose here: Normal people cool down by waving their hand in front of their face... Niewfies wave their face in front of their hands. Well... turns out this is pretty much the best way of detecting PWM on a flashlight (WAIT! There’s a twist to this... don’t risk blinding yourself or getting a neck injury before reading the rest!) Rather than waving your hand in front of your light, wave your light in front of your face. NOW, PWM will be easiest to detect on you light’s lowest mode (remember about duty cycle? Lower duty cycle = more space between pulses.) Second, you don’t need to send the lights directly into your eyes... just hold it so you can see the light on the side of the reflector as such:






Turn the lights down if necessary, so you can see the light clearly enough and now wave it sideways like this:






This is a picture of a constant current light. Any of your lights on maximum current should look exactly like that. 

Here’s a picture of bad PWM:





(Note: please respect your articulation’s limits... if you can’t see it, it might not be there)

Notice how we can see individual and separate spots of the same light’s business end? And I wasn’t moving very fast at all... In this case, just waving your hand or fingers in front of it will reveal the PWM even with a certain amount of ambient light.

Here is what “good” PWM looks like:






Let’s zoom-in on that picture:






This type of high frequency PWM is very hard to detect and is very unlikely to affect you under any circumstances; It can only be detected efficiently using this precise method and a camera also helps if you can catch your hand in just the right time.



What Are The Other Uses For PWM?

PWM is mainly used to control electric motors (like hybrid cars), but mostly step-motors like the ones in your hard-drive. 

Tons of newer cars have LED’s for daylights and rear position lights. As we all know the very same rear position lights are often also used as brake lights, so these lights need to be dimmed to differentiate from when a driver applies the brakes. Some manufacturers –perhaps most?- use PWM to achieve this, but some of them use a very (or failry) low frequency of PWM that actually affects some people, like me. I believe there is a more and more urgent need to sensitise manufacturers as the effects can be very uncomfortable for the eyes of some people. Just as an example, when I drive at night behind some models of Cadillacs or Volvo’s, I either slow down drastically to let them out of my sight or pass them as fast as reasonable (sometimes over the local speed tolerance) because it tires my eyes badly.


WHY PWM?

Using PWM to control a light’s output is simply cheaper, because so many existing Integrated Circuits sold off-the-shelves can do it and all that’s left for the manufacturer is to add a small circuit that controls the Duty Cycle or frequency. There is very little measuring, calculating, tweaking and experimenting needed from the manufacturer’s engineering department, so money is saved on manufacturing, parts AND research.


Conclusion

Well, there you go. Feel free to ask questions and I’ll answer to the best of my ability. Also, feel free to share your take on PWM, whether you’re a beginner or an expert on the subject. This could also be a good place to list light that are controlled by PWM and how much it shows and affects usage.


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## shane45_1911

Edited.

Thanks for a good explanation.


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## CarpentryHero

LoL that was a great description. Most Newfie jokes come from newfoundland, it's there second largest export. (there largest export being hard workers to Ft Mcmurry Alberta) 

I misspelled as seen below ⇓ 


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## Cataract

CarpentryHero said:


> LoL that was a great description. Most Newfie jokes come from newfandland, it's there second largest export. (there largest export being hard workers to FtMcmurry Alberta)


 
Kinda ironic with such a similar name...


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## shane45_1911

Cataract said:


> Sorry man, didn't mean to offend anyone here. I removed that comment.


 
We're cool. I have edited my initial post as well, as my comments were slightly skewed because of your comment.

Good summary on PWM. And thanks.


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## tre

Nice job explaining PWM. There have been a lot of PWM related threads recently and a lot of people thinking it is all bad. I have no problem with it if the frequency is high enough. My Zebralight SC51w has very slow and noticable PWM on the lowest mode. Oddly my other Zebralights have no such "slow PWM" on their lowest modes. Anyway, my point is that now people should understand PWM, and realize that it is not a problem (if it is fast enough).


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## Flying Turtle

Nice work, Cataract. I'm sure this has helped a lot of folks. I'm only bothered a bit by PWM, but I'm glad to see it less and less.

Geoff


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## Cataract

shane45_1911 said:


> We're cool. I have edited my initial post as well, as my comments were slightly skewed because of your comment.
> 
> Good summary on PWM. And thanks.



Well, you did make me realize it wasn't the best way to put it...
Thanks for correcting you post as well.


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## uplite

Great idea for a thread.

I'll add a few practical implications for flashlight buyers:

*1) PWM controlled lights can be made cheaper and smaller* than current-controlled (CC) lights, because the circuit is cheaper and smaller. This is why many of the little AAA-powered lights use PWM.

*2) CC lights give more consistent output from light to light*, because LED output is very closely correlated to current. PWM circuits use a fixed voltage. Since an LED's voltage-current response varies from batch to batch and even within the same batch, different LEDs will produce different amounts of light at that same voltage.

*3) CC lights are more efficient than PWM*, because LED efficiency increases at lower drive levels. A PWM light switches the emitter on and off at a single high (less efficient) drive level.

*4) PWM lights are less susceptible to tint-shift at low output levels*, because (as just mentioned) they are actually using a high drive level at all times (just switched on & off very quickly). This is why CC lights tend to shift towards green at low output levels. Especially with the new larger die emitters like XPG and XML.

*5) Higher frequency PWM is harder to see, but is also less efficient* than low frequency, due to switching losses in the circuit. This is not really an issue because if you care about efficiency, you'd use a CC circuit in the first place, but worth mentioning.

In brief:

If you care mostly about efficiency, ultra-long "moonlight mode" runtimes, and consistent output levels, then a fully current-controlled light is best.

If you care more about tint than moon-mode runtime, then the ideal design uses CC for high/medium modes, and PWM for the lowest modes.

-Jeff


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## shane45_1911

OK, how does one know if they are buying a light with PWM if they do not have access to an oscilloscope? I have never seen any Mfg. specs that indicate their light is (or isn't) PWM driven.


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## Cataract

shane45_1911 said:


> OK, how does one know if they are buying a light with PWM if they do not have access to an oscilloscope? I have never seen any Mfg. specs that indicate their light is (or isn't) PWM driven.



Very few manufacturers will mention driving their light through PWM. That's one of the reasons I always do heavy research on CPF before buying most of my lights. If you want to know if a light in your possession is PWM driven, take a look at the last two pictures in my first post. Very easy to check for yourself - you don't need a camera, just a little observation and as little ambiant light as possible.


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## tre

uplite said:


> *3) CC lights are more efficient than PWM*, because LED efficiency increases at lower drive levels. A PWM light switches the emitter on and off at a single high (less efficient) drive level.


 
You make a lot of good and valid points. I'm not saying you are wrong at all but how do you think Zebralight has such massive efficiency when using PWM? The SC51 which uses PWM is more efficient than a quark AA which is CC


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## shane45_1911

Cataract said:


> Very easy to check for yourself - you don't need a camera, just a little observation and as little ambiant light as possible.


 
Yeah, sorry - I totally missed your obvious description for checking for PWM. Been a long week...

Thanks again.


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## mhphoto

Excellent explanation and demonstration!

I've noticed that all of my 4Sevens current controlled lights have some "dithering" (or so I've heard it called) that appears similar to low frequency PWM on one or more of the lower levels. Do you have an explanation for that, because it's a bit annoying to me. Seems like current controlled lights on fresh primaries shouldn't have any trouble not blinking. :sick2:


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## Cataract

mhphoto said:


> Excellent explanation and demonstration!
> 
> I've noticed that all of my 4Sevens current controlled lights have some "dithering" (or so I've heard it called) that appears similar to low frequency PWM on one or more of the lower levels. Do you have an explanation for that, because it's a bit annoying to me. Seems like current controlled lights on fresh primaries shouldn't have any trouble not blinking. :sick2:



Do you mean some sort of a flicker? if that's the case, dirty threads and low batteries are the most common suspects. You shouldn't notice any strobe effect on current controlled lights. 
Don't forget that Quark mini's are PWM driven, but it's a very high frequency that's very hard to notice. In fact that is what I used in the last two pictures.


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## Cataract

BTW, thanks for all the compliments guys, and thanks for all the extra info, uplite. 

If anyone wants to add to this, I might regroup all the info in the original post so newbies can get everything out in one reading in the future.


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## mhphoto

Cataract said:


> Do you mean some sort of a flicker? if that's the case, dirty threads and low batteries are the most common suspects. You shouldn't notice any strobe effect on current controlled lights.
> Don't forget that Quark mini's are PWM driven, but it's a very high frequency that's very hard to notice. In fact that is what I used in the last two pictures.


 
No, it's definitely not dirty threads or low batteries (although I've documented that my S2 Turbo, which exhibits the blinking symptoms on the third level, also starts exhibiting it on the second brightness level when the batteries get low. With fresh batteries the second level is constant). There's a thread on it somewhere but I can't find it. I'll try to dig up a picture.


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## mhphoto

Here's a picture I took of a 123² Tactical (R2) before I sent it back because the flickering was so bad. 






On the left is "moonlight mode", middle is "low", and on the right is "medium". "High" and "max" showed no flickering. 

After I got so fed up with the flickering I sent it back and got the S2 123² Turbo, which as I said, flickers on the "medium" level. My 123² Tactical warm white flickers on "low" and "medium", and my RGB neutral flickers on "moonlight".

I have a Mini AA and its PWM is much higher frequency than the flickering coming out of the Quarks.

From what I remember about the thread that discussed this issue, the flickering is not so much a sharp "on and off" cycle, but rather an "on and fade" cycle.


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## Cataract

Nice picture! that's almost art, but what is shown here is definitely PWM. I have never seen such bad PWM on any of my 4sevens lights, but there are people who could say a lot more about 4sevens and the use of PWM.


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## afdk

:huh: PWM can be easily seen by pointing your light at your shower head, with water running of course! The water may look like separate drops depending on the PWM frequency. My Pelican 9410 does use PWM for the lower mode, but it is of sufficient frequency that it's only noticeable in the way described.

Try this with your lights, let me know what you see.


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## mhphoto

afdk said:


> :huh: PWM can be easily seen by pointing your light at your shower head, with water running of course! The water may look like separate drops depending on the PWM frequency. My Pelican 9410 does use PWM for the lower mode, but it is of sufficient frequency that it's only noticeable in the way described.
> 
> Try this with your lights, let me know what you see.


 
A ceiling fan works too 

The explanation that was given for the blinking on the Quarks involved graphs and such to show that, while it looks like PWM, it has a different signature on an oscilloscope (or whatever that neat machine is called).


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## indychris

Incredible description and illustrations, Cataract. For a newbie like myself who wasn't even aware that PWM existed, this was a huge eye opener.

So is that any type of near comprehensive list that notes which popular lights utilize PWM and those that do not?


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## Cataract

Thanks, I took my time coming up with this one and I'm glad people appreciate it.

There are no lists that I know of, but this would be a good time to start one. Of course, such a list should be split in two to separate the lights that show "good" and "bad" PWM, unless "someone" could measure the PWM frequency and include it in the list  :devil: 

If no one offers any help with this, then this thread would be a good place to start listing those lights. Later, I could compile the list and append it to the original post or put it in a separate thread.


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## The Shadow

Nice work Cataract!


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## mhphoto

On the subject of "good" and "bad" PWM (in my opinion):

Good: 4Sevens' Mini line, Newer Maratac AAA lights (just got my Copper AAA today )

Bad: Princeton "Fuel" headlamp. Its PWM is ridiculous. If it were any slower it would just be a strobe. Makes me nauseous just thinking about it… :sick2:


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## calipsoii

Great thread, very informative. The important thing to stress to people reading this is that PWM isn't inherently bad. Low frequency PWM is bad, yes, but if done properly (over 1000hz preferably) it's unnoticeable.

If you gave me a choice when ordering a multi-mode light: high-frequency PWM or current-controlled, I would choose PWM. There's nothing I hate more than a light that's a crisp, pure color on High and then suddenly goes to an ugly green when dropped down to Low.

(I'm looking at you, Preon Revo on my keychain)


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## Burgess

Great thread here !


Thank you, Cataract !


:goodjob::kewlpics::thanks:lovecpf
_


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## Burgess

BTW --

David (4Sevens) wrote (November 2009) this very interesting & informative post, 
comparing and contrasting PWM vs. current-regulation.


Here is the Link


Nice to have all this great info in one place !


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## Woods Walker

Nice work.


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## LedTed

Nice article Cataract! :twothumbs

Here is a trick you probably already know, to "look at" PWM. Shine the beam at the water from an indoor faucet.


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## mrlysle

GREAT thread Cataract! BTW, most, if not all of selfbuilts' reviews show the PWM frequency used and the respective output level for lights that use PWM. Some interesting reading there for those interested!


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## LukeA

Excellent post. 

One relatively inexpensive way to measure PWM frequency is with an RC airplane propeller tachometer, which uses a photocell to measure pulses of light and dark caused by passing blades. Set it for a 2-blade prop and multiply the rpm number by 2 pulses per revolution/60 seconds per minute to get the frequency in Hertz. 

Or, using a photograph, you can calculate frequency by counting the number of pulses and dividing that number by the picture's exposure time in seconds. In the first image in the OP, there are 8 pulses shown in a time of 1/8s for ~64Hz.


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## CarpentryHero

Cataract said:


> Kinda ironic with such a similar name...


 
Haha look at me miss spell lol


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## uplite

tre said:


> how do you think Zebralight has such massive efficiency when using PWM? The SC51 which uses PWM is more efficient than a quark AA which is CC


Good question.

Are we comparing apples to apples? What output level? Emitter? Battery?

I haven't looked in a while, but I seem to remember that Zebralight quoted their runtimes from a NiMH cell, and Quark used an Alkaline.

If the output, emitter, and battery are the same, then it comes down to the driver. There can be big differences in efficiency based on the quality of the components and circuit design. Perhaps Zebralight uses a better quality driver.

-Jeff


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## Sparky's Magic

Thanks Cataract! An excellent presentation. :goodjob:


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## HooNz

Use a portable shortwave receiver if it has a LW (longwave) on it , turn on the light , hold it close to the Rx'er , tune about to find a strong noiseless signal , turn off the light and if the signal disappears that would be the PWM frequency , then just to make sure with the light on tune about in that area to see if there is a stronger signal ..

Mine is 380khz or so , i posted this up yonks ago somewhere , i have seen mentioned over the net over a few months 12khz , 30khz , 60khz and up to around 1 mhz for PWM. 

And obviously if there is no signal the torch might not be PWM .


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## Cataract

mrlysle said:


> GREAT thread Cataract! BTW, most, if not all of selfbuilts' reviews show the PWM frequency used and the respective output level for lights that use PWM. Some interesting reading there for those interested!



I had a feeling he might state something in there, but got too lazy to go check. Thanks, I'll append that to the original post, among a lot of good info being shared here.




HooNz said:


> Use a portable shortwave receiver if it has a LW (longwave) on it , turn on the light , hold it close to the Rx'er , tune about to find a strong noiseless signal , turn off the light and if the signal disappears that would be the PWM frequency , then just to make sure with the light on tune about in that area to see if there is a stronger signal ..
> 
> Mine is 380khz or so , i posted this up yonks ago somewhere , i have seen mentioned over the net over a few months 12khz , 30khz , 60khz and up to around 1 mhz for PWM.
> 
> And obviously if there is no signal the torch might not be PWM .



The RC plane tachometer was a good one, but this is amazing! I don't have a shortwave radio, so I couldn't try it, but I knew there was something to do with this when I turned some of my lights on and off and my old tube TV lost the signal for half a second... I'm just finishing upgrading everything to digital and now you'll have me buy a shortwave/longwave radio...


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## Joe_Beam

This is a great thread. I have been wondering how pwm would affect shortwave/ longwave am radios. Now I would like to have somebody explain the different types of current regulation.


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## HooNz

Cataract said:


> I had a feeling he might state something in there, but got too lazy to go check. Thanks, I'll append that to the original post, among a lot of good info being shared here.
> 
> 
> 
> 
> The RC plane tachometer was a good one, but this is amazing! I don't have a shortwave radio, so I couldn't try it, but I knew there was something to do with this when I turned some of my lights on and off and my old tube TV lost the signal for half a second... I'm just finishing upgrading everything to digital and now you'll have me buy a shortwave/longwave radio...



LOL , if i was wealthy i would! , there are some good SW rx'ers out there , some get down to 15khz , some really good old ones that can be got cheep at secondhand shops or even garage sales (yard sales there?) , EE/bay is a spot too .  . I go to/Visit the "Special shop" .

ps-Technically if one wanted to really tune about , a VLF combination rx'er would be the go 1-400khz .


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## robostudent5000

seems like this thread is worth a sticky.


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## PEU

I made this video many years ago, you can see a clear visual explanation of PWM: http://www.youtube.com/watch?v=QI5JAt7vjNY


Pablo


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## jhc37013

I think that is the most informative PWM thread I've yet to see and I learned a couple new things thanks to the graphs and descriptions. Thanks.


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## tolkaze

I'm glad you mentioned 2 of my pet peeves, reading with PWM and cars and trucks with PWM controlled tail lights. I tend to get motion sick if do either of these. I love the low level of the zebralights for reading in bed when I don't want to disturb anyone, but PWM makes your eyes jump from word to word and the page stutters somewhat. I have to use the slightly higher level which IS current controlled to eliminate this. 
Makes me think that zebralight either has 1 full power mode, 2 high frequency PWM modes and 3 low freq PWM modes, or if they have 3 current controlled modes and then a PWM driver to lower each of those modes in turn (more likely). Either way, reading is a pain on the lower of any of the modes and perfectly fine on the others. 
Driving behind cars with those lights makes me sea sick... yechh surely if they are using multiple LED's (5mm for example) they could have 3 or 4 for running lights which are diffused through the plastic, then when you put on the breaks it lights up another 10 or so, also diffused. PWM seems like it ISN'T the easier option in this case.


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## Cataract

PEU said:


> I made this video many years ago, you can see a clear visual explanation of PWM: http://www.youtube.com/watch?v=QI5JAt7vjNY
> 
> 
> Pablo



Nice! I didn't even suspect a camera would show it this nicely!



tolkaze said:


> I'm glad you mentioned 2 of my pet peeves, reading with PWM and cars and trucks with PWM controlled tail lights. I tend to get motion sick if do either of these. I love the low level of the zebralights for reading in bed when I don't want to disturb anyone, but PWM makes your eyes jump from word to word and the page stutters somewhat. I have to use the slightly higher level which IS current controlled to eliminate this.
> Makes me think that zebralight either has 1 full power mode, 2 high frequency PWM modes and 3 low freq PWM modes, or if they have 3 current controlled modes and then a PWM driver to lower each of those modes in turn (more likely). Either way, reading is a pain on the lower of any of the modes and perfectly fine on the others.
> Driving behind cars with those lights makes me sea sick... yechh surely if they are using multiple LED's (5mm for example) they could have 3 or 4 for running lights which are diffused through the plastic, then when you put on the breaks it lights up another 10 or so, also diffused. PWM seems like it ISN'T the easier option in this case.



I don't have too much of a problem reading with a PWM controlled light, but whenever I see a Caddy or Volvo at night, I either have to slam the brakes or pass them like crazy, otherwise I go cross-eyed and risk an accident. Those are real bad PWM lights that tire my eyes really bad. I think the government should step in and impose some form of regulation on those.


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## Cataract

Have to mention this one brought up by Hexbright:


hexbright said:


> The higher the PWM frequency the higher the switching losses.


 
In other words, a high enough frequency that would be basically impossible to perceive would have a cost in battery life.


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## EngrPaul

*You can measure the frequency of PWM if your multimeter has a "Hz" model and you have a solar cell.*
 
*If you need a cheap solar cell, get a $1 solar calculator from Wal*Mart and rip into it.*
 
*Just connect the 2 solar cell wires and aim the flashlight at it.*
 
*You can also try using an LED. I found red usually works pretty well. But the solar cell works better.*


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## Richub

One of the torches with a bad PWM is the Olight M30 triton.

I bought one 2 years ago, only to shove it in a closet within a few months... On turbo it's simply amazing, but the sub-100 mhz PWM is damned annoying (and even nauseating) when I use the light on medium or low setting.

If I knew then what I know now about PWM, I wouldn't have bought that M30 at all.

My Fenix LD01 uses PWM on the lower settings, but at a very high frequency. This kind of PWM isn't bothering me at all. It's only noticable when waving the torch quickly in front of my face.


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## mhphoto

Found another horrible PWM light: Mini Maglite LED. It's baaad.


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## anylau

SO now i understand what PWM means... actually I use my table fan to detect PWM drive (back then i dint know it's call PWM.. i just tot is somesort of hz controlling drive..)
.. Another light using PWM is my *LED Lenser M7 *on the low adjustable mode....


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## DevL

I have 2 H51w headlamps, have seen low frequency PWM stutter before, and cannot notice it in either of my lights, which I recently purchased. Its a total non issue.


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## Cataract

I wrote to Zebra not long ago, concerning the two PWM driven modes on their lights (only 2 of the secondary modes use PWM, the rest are current driven) and they said they're using a 3-4Khz frequency on the newer models, so it should be very hard to detect and it is very unlikely that anyone will notice anything while using the light. The older revision does use a lower frequency PWM and some people have reported avoiding those modes.


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## archer6817j

Reviving this thread  So in terms of implementation...what's the difference between "good" and "bad" PWM? If it's just a matter of frequency, wouldn't all lights be "good" at high power and "bad" at low power? Obviously I don't know that much about the ins 'n outs so that's why I'm asking  

I'm looking into drive options for my lights and I can't seem to figure out what exactly separate good from bad.


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## tam17

Great thrad indeed.



archer6817j said:


> ...what's the difference between "good" and "bad" PWM? If it's just a matter of frequency, wouldn't all lights be "good" at high power and "bad" at low power? Obviously I don't know that much about the ins 'n outs so that's why I'm asking
> 
> I'm looking into drive options for my lights and I can't seem to figure out what exactly separate good from bad.


 
From the end user's point of view, "good" PWM is the one that doesn't bother you, and the "bad" one is... well, the opposite.

Apart from Cataract's informative opening post, Uplite stated some practical implications of PWM and CC for flashlight buyers.

Cheers,

Tam


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## GaAslamp

archer6817j said:


> Reviving this thread  So in terms of implementation...what's the difference between "good" and "bad" PWM?



I gather that it's frequency. In visual terms, the higher the switching frequency, the less visible the strobing effect will be, and that's good. On the other hand, higher frequency is less efficient, so obviously a happy medium must be found if you're going to use PWM at all--just high enough to avoid being detected during normal use.



archer6817j said:


> If it's just a matter of frequency, wouldn't all lights be "good" at high power and "bad" at low power?



Not in the way you're thinking because it's not frequency that determines the overall lighting level but the pulse width or duty cycle--basically how long the emitter is switched on, proportionally, during each cycle, regardless of the frequency. It should be noted that a 100% duty cycle means that the emitter is always lit, so it's always going to look good regardless of frequency, and that for a given level of visual quality higher frequencies are necessary for lower power modes because the emitter spends so much time unlit contiguously, given the low duty cycle.



archer6817j said:


> Obviously I don't know that much about the ins 'n outs so that's why I'm asking



That's alright because I thought I understood this stuff pretty well, but am now kind of confused myself after reading this thread. 

This might get slightly technical , but what's bugging me is that PWM and CC (current-controlled using buck, boost, or buck-boost converters) are being described as two fundamentally different things, while I've always viewed them as being sort of the same thing, only with CC being filtered using inductors and capacitors. They both have digital switches that operate at a certain frequency and they both operate on the basis of duty cycle (like switching power supplies)--the difference is that CC "smooths" the on-off pulsing down to a set of more steady intermediate voltages which results in a corresponding set of fairly constant intermediate currents to feed the emitter.

While I grant that the effects are fundamentally different once the outputs of these circuits (PWM and CC) reach the emitter, I still think they're basically the same thing--CC being a more refined form of PWM, in a way--which is evidenced by the "flickering" or "dithering" that people have been noticing on the Moonlight mode of Quarks, which is really, at least according to my understanding, just some electrical ripple from imperfect filtering (it's tough to do well with such a low duty cycle). That's right, unless there is a major problem with my understanding, the "flickering" is basically the underlying PWM leaking past the filtering, so to speak. That's probably why nobody else uses CC for such low-power modes--what's the point if it's going to flicker anyway and change the tint of the beam in addition? There's an efficiency gain at the emitter, yes, but some loss as well from the additional circuitry. That's probably why ZebraLight, for example, uses PWM for their comparably low modes, despite the fact that they use CC for most every other mode, and interestingly enough they're getting just as much overall system efficiency in those super-low modes.

Anyway, I wonder now if the foregoing is just plain wrong because I don't understand this stuff like I thought I did, but it still makes sense to me. :shrug:



archer6817j said:


> I'm looking into drive options for my lights and I can't seem to figure out what exactly separate good from bad.



Generally CC is better because it's almost always more efficient (at the cost of higher price and more circuitry), but PWM can be made to work practically as well (or it could be quite bad in some cases). It's just one factor, and to properly evaluate different flashlights you'll need to read reviews (some of which on this forum contain rather sophisticated and comprehensive performance testing :rock: ) and anecdotal accounts of real-world usage.


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## archer6817j

So frequency is the time between pulses and the duty cycle is the time the LED is on during each pulse? 

In that case, to minimize dithering in low modes, the frequency should be high and the duty cycle should be low? ... with the caveat that high frequency is less efficient. What is the range of efficiency we are talking about as it would affect total battery life? I realize it's "less" efficient on paper but I'm wondering what the actual real world result is


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## AFKAN

Got to say a cracking thread 

I too have noticed a few cars using pretty poor PWM on their rear lights 

I can see it so badly I pretty much want to puke after a short time


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## precisionworks

Nice writeup Cataract :thumbsup:

Almost all newer industrial motor controls (frequency drives) use either PWM, or they use a more sophisticated logic device known as "frequency vectoring". PWM drives are sometimes called Volts/Hz as the higher the volts, the higher the freq - full voltage is seen only at one set freq, and voltage drops as freq drops.

Vector drives monitor motor shaft position (to determine if the shaft is lagging behind where it should be) and boost the output freq as needed. Flashlights are not quite as difficult to control as a 3-phase motor, but continuing development of the microprocessor makes a flashlight vector drive a possibility - in the future.


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## mat_the_cat

precisionworks said:


> flashlight vector drive


 Now that's a catchphrase to appeal to the layman!


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## GaAslamp

archer6817j said:


> So frequency is the time between pulses



Technically it's the inverse, expressed in pulses or cycles per second (Hz), but you have the right idea.



archer6817j said:


> and the duty cycle is the time the LED is on during each pulse?



That's right, and it's in proportion to the duration of each pulse (the inverse of the frequency).



archer6817j said:


> In that case, to minimize dithering in low modes, the frequency should be high and the duty cycle should be low? ...



You got it.



archer6817j said:


> with the caveat that high frequency is less efficient. What is the range of efficiency we are talking about as it would affect total battery life? I realize it's "less" efficient on paper but I'm wondering what the actual real world result is



I do, too.


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## davidV5

Very useful information. Thanks for digging up this thread.


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## archer6817j

So I know linear drivers like the battery voltage to be close to the led Vf...but what about pwm? Could I get a pwm driver to handle the range from 3-12V? What would be the advantage/disadvantage?


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## hazna

I missed this thread the first time it was posted. Good explanation of PWM.

I find I am quite sensitive to PWM. Even on lights that have higher a PWM, I can sometimes notice the flickering from the corner of my eyes when I move my head.


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## odd

@archer6817j
You could use a buck driver to convert the V_in(3-12V) to V_out(3,6V) and a µC+MOSFET for PWM.

Buck/buck-boost drivers usually are more complex and thus bigger and more expensive.
But you can use a wider voltage range at a decent efficiency.


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## precisionworks

odd said:


> @archer6817j
> You could use a buck driver to convert the V_in(3-12V) to V_out(3,6V) and a µC+MOSFET for PWM.
> 
> Buck/buck-boost drivers usually are more complex and thus bigger and more expensive.
> But you can use a wider voltage range at a decent efficiency.


 I certainly appreciate your clear explanation. Flashlight electronics are still a mystery to me. My knowledge of buck and boost is limited to control transformers and isolation transformers, where they are used to slightly raise or lower a critical voltage.


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## Darvis

Incredible thread...

I was searching about for info on PWM as I had been noticng it on two recent lights that I purchased. I suspected that I might be a tad more sensitive to the effects as I posted about the PWM I was seeing and one member confirmed he had not noticed it at all.

I did the "good" vs "bad" PWM tests, and by all acounts, the PWM is good, but I still really notice it, especially when I catch reflections as the result of movement off of reflective surfaces like chrome, etc.

Anyway, the two lights are my new McGizmo XM-L Mule and the Oveready Triple XPG H-M-L head. I'd be curious if anyone else is seeing this on either of these lights?


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## Kinnza

Very good thread about PWM, Cataract.

I would like to add a nuance to the initial post 



Cataract said:


> As you can see, we have now changed our constant voltage input for a square wave. In this graphic, our voltage is on half the time and off half the time. The technical term here would be that we have a 50% duty cycle (50% of the time on.) With such an input on our LED, the amount of light given off appears diminished by 50%. The reason I say it appears, is because it gives off its maximum amount of light, but only 50% of the time, so our eyes perceive only half the amount of light (more on this in the next section).



It would be more exact to say

"With such an input on our LED, the amount of light given off appears diminished as much as 50%" or "With such an input on our LED, the amount of light given off appears diminished by 50% if there is no any flickering"

The reason lies on the Broca-Sulzer effect that states that when light pulses are short enough (below 0.1 or 100ms, but usually 50ms and less), perceived brightness is enhanced. How much it is enhanced depends of the frequency, pulse duration and overall true brightness level, but its often of 30-40% and can reach more than 200% (perceived brightness more than double than actual).

This effect is due to human visual system not being a perfect integrator of light and it's related to the own flickering effect. When there is no flickering, there is no Broca-Sulzer effect. So its just a nuance because if the system is designed to avoid flickering fully, the initial statement is right. Actually, with this explanation, I think there is no need to edit initial post.

But I think it is worth to point out it because when a small flickering is tolerated, it is possible to get an enhancement on perceived brightness by using PWM, being able on some situations to overcome the inherently more efficient way of Constant Current dimming (at least, considering LEDs alone, and not efficiency of the driver/compatibility with batteries).


----------



## Cataract

I revive this thread to thank Bullzeyebill for making this a sticky. 

I also encourage everyone to share their own experience on PWM detection and good or bad experiences with specific PWM frequencies.

I also see my picture links in post 1 have somehow been corrupted and will update them when I get a chance, probably next weekend.


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## greatscoot

Cataract. Thanks in advance for reposting pics, etc. I just found this thread and was going to ask if you could do that.

As for PWM, I just started to notice this in some of my lights. The first time was when I was walking back to my house and caught the reflection off of the parked cars reflectors out of the corner of my eye. I thought it was just from the reflection, but started to notice it more frequently. When I saw that I did the very unscientific experiment of pointing the lights at a moving fan and you can see the different levels of PWM based on whether the light is on Low, Med or High (then I found out about the shower trick).

It seems that I am more sensitive to this now than I was before too. 

Cadillac tail lights for sure, really annoying.


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## Cataract

Pics have been updated.

greatscoot: you're welcome. The pics should definitely make things a lot clearer...

PWM is often easy to notice when your light shines back at you from reflective surfaces an you move our eyes or head around. Some lights, like Zebralight before they finally went for constant current regulation, are very nice to use in general but you still see the PWM on surfaces like a stainless steel faucet while moving about. 

I believe we tend to notice PWM more once we have seen the effects. I also notice a lot of newer cars (like Caddys and Volvos) seem to have gotten away from PWM tail lights (thank god!) but other manufacturers like KIA have started using it in their newer luxury models. It hopefully is only a matter of time before they get enough complaints and start doing things the sensitive way.


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## RI Chevy

It is odd for me to say, but I notice the PMW in my drop ins more from the high pitched whine rather than the flickering of the light. 
My ears supersede my eyes. 
The "whine" sound drives me battey. On the other hand, I have a drop in with a linear driver that does not show any effect of PMW at all. This I prefer.


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## Jakeyb

M​y eyes are very susceptible to pwm I notice it almost all the time even in the higher end lights. It's current controlled for me now a days


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## Cataract

RI Chevy said:


> It is odd for me to say, but I notice the PMW in my drop ins more from the high pitched whine rather than the flickering of the light.
> My ears supersede my eyes.
> The "whine" sound drives me battey. On the other hand, I have a drop in with a linear driver that does not show any effect of PMW at all. This I prefer.



Interesting, what brand of dropins? It is possible you have an ear that is sensitive to higher frequencies than most people - I do, but I have never _heard_ PWM so far and some of my lights have a PWM frequency that is definitely in the average hearing range.



Jakeyb said:


> M​y eyes are very susceptible to pwm I notice it almost all the time even in the higher end lights. It's current controlled for me now a days



Some people are extremely sensitive, but not all higher end lights use a high enough frequency for PWM to be unnoticeable. 

47's are the only ones so far that are just fine with me and I can endure the PWM regulated Zebras that I own, but they're borderline to me as I immediately notice it in reflections on the faucets. Those will be replaced with the newer current-controlled models as I can afford it...


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## RI Chevy

The drop in is my Malkoff M361N. The PMW is extremely loud in my particular drop in.


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## Cataract

Thanks. It could be an unusual inductor whine. I also have a few lights with high pitch sound, but I personally don't find it annoying and it has nothing to do with PWM. It would be interesting to know what frequency PWM is used and if others hear it as well.


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## RI Chevy

Everyone in my house can hear it. I am unsure on the frequency of the PMW, as I am only an end user and know nothing about the mechanics of it.  
But it is louder on medium than on low. Go figure.


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## Cataract

RI Chevy said:


> *Everyone in my house can hear it.* I am unsure on the frequency of the PMW, as I am only an end user and know nothing about the mechanics of it.
> But it is louder on medium than on low. Go figure.



OUCH! I hope you only mean they can hear it from a short distance, not wake up in the middle of the night while you're having a midnight snack! LOL

I only own one Malkoff and it only has one mode, but your case sounds unusual. Does the whine change pitch between modes? Do you still hear it on high?

I ask because it could be a regular (but not necessarily normal) inductor whine that has nothing to do with the PWM


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## RI Chevy

No. They can only hear it when it is close to their heads. But at a distance of about 2 to 3 feet. 

I have no PMW on high, PMW on medium, and PMW on low. But the thing is it is louder on medium than on low, and their is a different, higher pitch tone on medium than on low. Low is quieter and has a lower pitch tone.


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## Cataract

Extremely interesting stuff... do you hear it from farther away than the others? Does it annoy everyone just as bad? Do you (or anyone else) hear a whine on high? 

Note: High mode is not commonly controlled through PWM; high mode is usually current-controlled or direct-drive.


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## RI Chevy

Everyone can hear it and they don't like it.


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## Cataract

Even on high? If so, then I'd say there is a faulty inductor, or bad solder/trace inside...


----------



## jorn

The loudest light i have owned is a lumapower lm21. The noice from the pwm filled the room... The funny thing is i could hear it used way different frequencys on med and lo mode. Lo mode was growling in a lo pitch noice (crappy low frequenzy), medium mode was screaming in a higher frequency. A simple shaketest comfirmed it visually.


----------



## RI Chevy

RI Chevy said:


> No. They can only hear it when it is close to their heads. But at a distance of about 2 to 3 feet.
> 
> I have no PMW on high, PMW on medium, and PMW on low. But the thing is it is louder on medium than on low, and their is a different, higher pitch tone on medium than on low. Low is quieter and has a lower pitch tone.





Cataract said:


> Even on high? If so, then I'd say there is a faulty inductor, or bad solder/trace inside...



No PMW on high. Only on Medium and Low.


----------



## Cataract

jorn said:


> The loudest light i have owned is a lumapower lm21. The noice from the pwm filled the room... The funny thing is i could hear it used way different frequencys on med and lo mode. Lo mode was growling in a lo pitch noice (crappy low frequenzy), medium mode was screaming in a higher frequency. A simple shaketest comfirmed it visually.



Ouch! room-filling PWM noise is as bad and even worse to the ears as low frequency PWM to the eyes! 
Because of the square wave's shape, it should sound and look like higher frequency -in most cases- when using a higher output, but the frequency is normally the same. This is due to the time off being shorter at higher output, making it seem like the flicker happens more often (thing of a faster strobe, but in this case, it is only our perception that is tricked into believing that). Some light could use a different frequency for each mode, but that's not a very economic way to go as it means having more complex or just more IC's (chips) on the board.



RI Chevy said:


> No PMW on high. Only on Medium and Low.



I know it might have seemed like I wasn't paying attention, but a high pitch whine on high means an inductor is whining, not having anything directly to do with PWM as high is most often direct-current or current driven (think of the straight line in my graphs.) It still could come from a bad solder of faulty inductor (small copper wire coil) in your light but, seeing that it might not be an isolated case, it couldt be a side-effect of low frequency PWM as well... I never heard that in person but I take both your words for it. I definitely don't like PWM in all its forms, period, but PWM noise must be a total wretch!

So, there ya go: Another bad side effect of PWM could include annoying noise (perfect or faulty board and/or components and/or soldering or whatnot)


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## jorn

Frequency is not the same on lo and med on the lm21. Lo mode uses a really slow and easy to see pwm. Med is faster and harder to detect.


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## Cataract

I'm trying not to get too technical to keep the thread as simple as possible in the spirit of the original post:

They probably use 2 different chips with fixed frequencies and pulse width. 
Changing the frequency _instead_ of pulse width is also a means to change the perceived intensity: less "beats per second" will be perceived as dimmer than a higher (faster) frequency, but that also means it is guaranteed you will perceive the strobing effect very easily on lower modes. That is not really PWM, though, but it is the same basic principle. It makes for a much simpler circuit and possibly cheaper, but not necessarily smaller.


----------



## RI Chevy

Cataract said:


> I know it might have seemed like I wasn't paying attention, but a high pitch whine on high means an inductor is whining, not having anything directly to do with PWM as high is most often direct-current or current driven (think of the straight line in my graphs.) It still could come from a bad solder of faulty inductor (small copper wire coil) in your light but, seeing that it might not be an isolated case, it couldt be a side-effect of low frequency PWM as well... I never heard that in person but I take both your words for it. I definitely don't like PWM in all its forms, period, but PWM noise must be a total wretch!
> 
> So, there ya go: Another bad side effect of PWM could include annoying noise (perfect or faulty board and/or components and/or soldering or whatnot)



I got you.  I am not sure I could check the soldering on the M361N now though. Funny thing is I can't see the flickering, but I can hear the whine. I have 2 distinct whines on medium and low only. Just my luck.


----------



## Cataract

RI Chevy said:


> I got you.  I am not sure I could check the soldering on the M361N now though. Funny thing is I can't see the flickering, but I can hear the whine. I have 2 distinct whines on medium and low only. Just my luck.



Ah, things are clearing up now...

Malkoff drop-ins are potted, so you can't open them up. If you can't see any flickering, even using my technique or any other, then you might just have a noisy inductor. Doesn't mean your module is not using PWM for med and low (I don't know Malkoff devices all that well); the sound frequency from an inductor will change with different pulse widths, with a higher pitch for a wider pulse - or higher output as in medium mode. I could bet this is it, as I do have a hard time believing Malkoff was cheap enough to use a slow frequency modulation. There is however another possibility: a fit that is not even in the host could also cause high pitch noise on certain modes. Basically, the "vibration" can be transmitted through smaller contact points. The physics of this can be complicated to explain, so I prefer to leave it out at this point, but it has happened to me once and was cleared up with a good maintenance and rotating the dropin a bit (sounds like shameless self-publicity and cross-ref between my own stickies) Try these steps to see if it changes anything: Basic Flashlight Troubleshooting Guide (I should have started with that before elaborating, but I'm leaving all the good info on the thread.)

If that doesn't change anything, it could be interesting to start a thread on your specific drop-in and ask if anyone else has noise issues. Something tells me your case is exceptional and you might be able to get a replacement - provided the problem has not been solved with maintenance by now.


----------



## RI Chevy

Thanks for the informative response. I have it in a Surefire bored 6P. The fit is flawless inside the host, but I'll try a few of the tips and see if I get a different outcome. I have many, many Malkoff modules, and I really do not want to make a big deal out of it, as I have to much respect for the Malkoff's. All of my others are absolutely perfect. Thanks again.


----------



## Cataract

My pleasure, I think people deserve to know. 

I know about the Malkoff quality, so I find it a little odd. It is most likely a very exceptional case, but do let us know if maintenance makes any difference. If it does I would be grateful if you would mention it in the troubleshooting guide to share with others.


----------



## RI Chevy

I experimented with the M 361 N drop in and hosts that I have. Unfortunately I hear the PMW in any host I place it in while on low and medium power. So I think it is the drop in, not the host. The PMW is pretty consistent regardless of what host I place it in. I am running an 18650 battery.


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## Cataract

I'm pretty sure you have it cornered to the dropin. I'd take a chance and write Malkoff about this, they might just replace it.


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## dml24

Cataract, thank you for a simple to understand explanation. Excellent photos and graphics!


----------



## Cataract

Thanks, I did this all in the good spirit of CPF knowledge sharing :twothumbs:


----------



## weaver

First, thanks Cataract for a very informative description of PWM!



LukeA said:


> Or, using a photograph, you can calculate frequency by counting the number of pulses and dividing that number by the picture's exposure time in seconds. In the first image in the OP, there are 8 pulses shown in a time of 1/8s for ~64Hz.



Great tip, this may be the easiest method to measure PWM with fair accuracy with just a camera. With this, I was able to find the PWM of an Everest headlight to be about 110 Hz, which I find quite annoying in some situations, while the higher PWM of Lumapower LM31 on low mode is higher at about 675 Hz, which is not that noticeable in most situations.



jorn said:


> The loudest light i have owned is a lumapower lm21. The noice from the pwm filled the room... The funny thing is i could hear it used way different frequencys on med and lo mode. Lo mode was growling in a lo pitch noice (crappy low frequenzy), medium mode was screaming in a higher frequency. A simple shaketest comfirmed it visually.



Interesting, I bought a Lumapower LM31 recently, and there I can only hear a faint whine if I hold the light right next to the ear.


----------



## agnelucio

Any frequency above 5kHz is pretty much undetectable, unless you're using a slow motion camera. 

Although, if the frequency is 1kHz, and the duty cycle is 5%, then 1/1000=0.001, and 100/5=20, and 0.001*20=0.02, and 1/0.02=50.
So the light may appear to be flashing at 50Hz. Just thought I'd mention it.

Nice explanation by the way. :thumbsup:


----------



## weaver

agnelucio said:


> Although, if the frequency is 1kHz, and the duty cycle is 5%, then 1/1000=0.001, and 100/5=20, and 0.001*20=0.02, and 1/0.02=50.
> So the light may appear to be flashing at 50Hz.



If that was the case, then my LM31, with a PWM frequency of 675 Hz and a duty cycle of 1% on low, would appear to flash at about 7 Hz, which it doesn't. It still appears to flash at 675 Hz, while during every flash cycle the light is only on for 1% of that time.


----------



## reppans

I think this thread should have a disclaimer "if you want continue enjoying all your lights, please do not read." Before CPF, I never knew what PWM was, and I never saw it. Then I learned what it was, started looking for it, and even found very easy ways to detect high frequency PWM in every day scenarios and without equipment. 

Damn it, now I can't stop seeing it and it has all but ruined my taste for any light with it. It doesn't make me nauseous or anything, but it constant comes into my view and my brain instantly notices something unnatural that makes me do a double take... "Oh yeah, PWM" and then everything is back to normal. It's just plain annoying now, and has made quite a few shelf-queens of some good lights. 

Ignorance is bliss.


----------



## Cataract

agnelucio said:


> Any frequency above 5kHz is pretty much undetectable, unless you're using a slow motion camera.
> 
> Although, if the frequency is 1kHz, and the duty cycle is 5%, then 1/1000=0.001, and 100/5=20, and 0.001*20=0.02, and 1/0.02=50.
> So the light may appear to be flashing at 50Hz. Just thought I'd mention it.
> 
> Nice explanation by the way. :thumbsup:



Thanks!
I'm not 100% sure on your math, though (no time to pick up the calculator but I think you skipped a step), but yes, the shorter the duty time, the more it will _appear_ to flash, mostly because it is easier to detect. I think the correct interpretation of your math is not really that it will look like it is flashing at 50Hz, but that it should be as easy to detect as if it was...



reppans said:


> I think this thread should have a disclaimer "if you want continue enjoying all your lights, please do not read." [...]



LOL! I think you're right, though...



reppans said:


> [...]Before CPF, I never knew what PWM was, and I never saw it. Then I learned what it was, started looking for it, and even found very easy ways to detect high frequency PWM in every day scenarios and without equipment.
> 
> Damn it, now I can't stop seeing it and it has all but ruined my taste for any light with it. It doesn't make me nauseous or anything, but it constant comes into my view and my brain instantly notices something unnatural that makes me do a double take... "Oh yeah, PWM" and then everything is back to normal. It's just plain annoying now, and has made quite a few shelf-queens of some good lights.
> 
> Ignorance is bliss.



I noticed that with medium speed PWM you can enjoy blissing ignorance for quite a while. With slow PWM lights, though, you notice it very easily and it becomes annoying over time when you get used to have lights with non-detectable or no PWM at all. I was lucky enough to notice it early, L0D being one of my first lights, and have paid attention from there on, even though it does not make me sick either, but I understand the pain or shelving a perfectly functioning light. I use my L0D as a keychain light now, and my older Zebras will become beaters when I upgrade them as they only annoy me near reflective surfaces.


----------



## reppans

Cataract said:


> I noticed that with medium speed PWM you can enjoy blissing ignorance for quite a while. With slow PWM lights, though, you notice it very easily and it becomes annoying over time when you get used to have lights with non-detectable or no PWM at all. I was lucky enough to notice it early, L0D being one of my first lights, and have paid attention from there on, even though it does not make me sick either, but I understand the pain or shelving a perfectly functioning light. I use my L0D as a keychain light now, and my older Zebras will become beaters when I upgrade them as they only annoy me near reflective surfaces.



Interesting... my old Zebra H51w uses a PWM that's about the slowest I've ever seen on any light - it was the first to become a shelf queen. The Foursevens Minis uses a high frequency, but just as you have mentioned here and elsewhere, the reflections off glass, faucets, etc, are what constantly catch my eye for that annoying double-take - I can't use them any more. It's really not an issue outdoors with few reflective surfaces, but indoors, there always seem to be something that reflects back.

At a quick glance, I also didn't see any mention here of the cellphone PWM test. Here's an example of a current regulated 47s Quark, high frequency 47 Mini, and and low frequency H51w all taken with an iPhone (they're all on their lowest modes):


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## jorn

I notice outddors because it rains alot, so any wet surface can be reflective.. 
Hate the pwm flicker on tail lights on the newer cars. Slow pwm led lights should have been banned on cars. The faster the car in front of you moves, the more visible the pwm gets. In every curve, or bump in the road, the flicker from the tail lights grabs my attention. The roads around here are made of bumps and curves only


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## Cataract

reppans said:


>



Coool! That's a great visual!



jorn said:


> I notice outddors because it rains alot, so any wet surface can be reflective..
> Hate the pwm flicker on tail lights on the newer cars. Slow pwm led lights should have been banned on cars. The faster the car in front of you moves, the more visible the pwm gets. In every curve, or bump in the road, the flicker from the tail lights grabs my attention. The roads around here are made of bumps and curves only



...and also whenever you move your eyes around...ach! :duck: I do everything to avoid them; slow down, pass them or just take another street when possible. I do see less of them lately, but the age of darkness is upon us; what normally is a good time for flashaholism now has it's demon! I did notice that the worst ones (I prefer not to name the 2 specific brands here) seem to have remedied to that on newer models, but other makers are making the same mistake all over again. Hopefully there will be a law against that sometime soon... hopefully.


----------



## Yagon

mhphoto said:


> Here's a picture I took of a 123² Tactical (R2) before I sent it back because the flickering was so bad.
> 
> 
> 
> 
> 
> 
> On the left is "moonlight mode", middle is "low", and on the right is "medium". "High" and "max" showed no flickering.
> 
> After I got so fed up with the flickering I sent it back and got the S2 123² Turbo, which as I said, flickers on the "medium" level. My 123² Tactical warm white flickers on "low" and "medium", and my RGB neutral flickers on "moonlight".
> 
> I have a Mini AA and its PWM is much higher frequency than the flickering coming out of the Quarks.
> 
> From what I remember about the thread that discussed this issue, the flickering is not so much a sharp "on and off" cycle, but rather an "on and fade" cycle.





Cataract said:


> Nice picture! that's almost art, but what is shown here is definitely PWM. I have never seen such bad PWM on any of my 4sevens lights, but there are people who could say a lot more about 4sevens and the use of PWM.



Could that be a failed storage device (blown cap or inductor overheated and short cct) in the switching regulation ?


----------



## Cataract

Yagon said:


> Could that be a failed storage device (blown cap or inductor overheated and short cct) in the switching regulation ?



Yes, it could be a blown or defective component (also including frequency pulser), bad solder or cracked board whether the problem was from manufacturing, shipping/handling, overheat of even freeze. I dropped my 4 sevens lights many times with no such issue though, so I tend to think it was a defect from the manufacturing side. This kind of problem might be hard to catch during QC since the light generally behaves the way it should.


----------



## Yagon

Cataract said:


> Yes, it could be a blown or defective component (also including frequency pulser),



Do you mean the cmos switch ?
Thought that would either fail open or closed cct .
Doesn't have to mean a manufacturing error(of the flashlight) too , it could simply be a case of infant mortality of the component .


----------



## Cataract

Yagon said:


> Do you mean the cmos switch ?
> Thought that would either fail open or closed cct .
> Doesn't have to mean a manufacturing error(of the flashlight) too , it could simply be a case of infant mortality of the component .



Yes; I've seen CMOS and other types of clocks ticking at the wrong rate because of manufacturing defects or because the signal wasn't steady enough (because of a manufacturing defect again) for other circuits to function normally and even because of premature death of only part of the IC. Most of the time things are black and white with modern IC's, but not always...

And yes again, it could be premature death of some component. 4Sevens is not necessarily to blame on this, but a faulty solder or trace could possibly cause this type of problem too; I've seen weird stuff in my career. Without their blueprints on hand it is hard to rule out anything for sure, and even then... That's why manufacturers usually want to have the defective product back; so they can find out what went wrong and prevent it from happening again.


----------



## agnelucio

I don't think that dropping a light would cause significant damage to the electronics (except perhaps for a large inductor). Much more likely to be a dry/dodgy solder joint.


----------



## agnelucio

Cataract said:


> ..the correct interpretation of your math is not really that it will look like it is flashing at 50Hz, but that it should be as easy to detect as if it was...



Yes, sorry, that's exactly what I meant. (and should have said).


----------



## Cataract

agnelucio said:


> I don't think that dropping a light would cause significant damage to the electronics (except perhaps for a large inductor). Much more likely to be a dry/dodgy solder joint.



Very likely, but I've seen stuff happen. Since we do not know what was the actual cause, we can only propose theories which is not the scope of this thread (my bad for digressing so far out). Let's get back on track with PWM



agnelucio said:


> Yes, sorry, that's exactly what I meant. (and should have said).



:thumbsup:. We are only humans using keyboards


----------



## tattoosteve99

Just read through this. Excellent write for me. I was wondering about this and now it's clear. Thanks so much! 


Sent from my iPhone using Tapatalk


----------



## Cataract

Thanks Steve. Knowing I could make it clear for fellow CPFers makes my day :twothumbs


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## hjdca

afdk said:


> :huh: PWM can be easily seen by pointing your light at your shower head, with water running of course! The water may look like separate drops depending on the PWM frequency. My Pelican 9410 does use PWM for the lower mode, but it is of sufficient frequency that it's only noticeable in the way described.
> 
> Try this with your lights, let me know what you see.



I tried this with 5 four lights: Draco (Flupic), Haiku (GDuP, 4 level), Mac's Tri-EDC, Jetbeam TC-R1, & P60 dropins for my TnC from Vinh and Nailbender... The Draco with Flupic had the worst PWM on low and user defined settings.. Very choppy... On high, there was no PWM... The Haiku with the GDuP driver had no perceptible PWM on any level except some slight "chaining" at 10 ma... At 200 ma all the way up to 1200 ma, there was no PWM... The TC-R1 had no PWM at any level, even the very, very low settings had no PWM... Mac's Tri-EDC and the P60 dropings from Vinh and Nailbender behaved exactly the same.. High quality, high frequency PWM at low and medium levels and no PWM on high... The PWM at these lower levels was excellent, just some high speed "chaining".... This experiment really makes me appreciate the GduP driver and the TC-R1 driver... Thanks for the tip !!


----------



## hjdca

hjdca said:


> This experiment really makes me appreciate the GduP driver and the TC-R1 driver... Thanks for the tip !!



Actually, I am more impressed with the GDuP than the TCR1 because of the buck, boost drivers... The GDuP will do its thing with a primary and a rechargeable... The TCR1 does not have this capability and you have to use a rechargeable... Other DC engines from China also seem to be missing buck drivers..., ie. you put a 4.2 volt rechargeable in it and all you get is high, like Fenix...


----------



## Hondo

Yagon said:


> Could that be a failed storage device (blown cap or inductor overheated and short cct) in the switching regulation ?



Check my post at the end here, along with others observations:

http://www.candlepowerforums.com/vb...Question-on-Quark-Tactical-and-PWM&highlight=

This is more than one or a few lights with bad components, and David considers it normal, and not PWM. It is apparantly "warble" in a constant current controlled circuit. It is interesting as it seems to be the only case of a non-PWM controlled light looking exactly like a PWM light, and at a fairly low frequency. The reduction to 30% brightness rather than 0% as in true PWM does not seem to lessen the effect noticeably. Just when you thought you were safe from flickering lights by ordering a 100% current controlled light, there comes an exception.

My interest in the other thread centers on the different flavors of this circuit. Most Pro interfaces seem steady, but I have one that all three of the lowest levels do it. Most reports are for the Tactical interface, and only on the low and medium. But there are also plenty of the same lights without the phenomenon.


----------



## Cataract

Thanks Hondo, I was just about to point to that resuscitated thread. Even though the flickering effect in Quarks is not supposed to be PWM per se, our eyes perceive it as the exact same phenomenon and the effects on perceived light intensity will obey the same law of average output. Usually, though, this flickering in Quarks is very high frequency (at least in all of my numerous Quarks) and very hard to see, as pictured in my original post:






Anything significantly noticeable sounds unusual to me and I too would find it very annoying.


----------



## Hondo

I managed to grab this image of three lights. The one on the left is my Quark 123^2 Tactical, wearing a filter to remove green and make it more neutral. The center is an ITP A2 Eos, known to be in the 2K+ Hz range. The last is the notorious 100 Hz Fenix L0D. They are all on their medium level.







I would give the Quark, based on the Fenix being 100 Hz, about 350 Hz. I somehow don't get the graph linked by cave dave in the other thread, as it shows a full cycle in what is labeled about 0.5 ms, which would be 2 kHz. Yet he says it supports his guess of about 200 Hz. That was measured by HKJ, and I am guessing it is the non-objectionable artifact that David speaks of in a light which does not exhibit this "PWM-like" behavior.

Here is another pic with just the Quark, in which I really cranked up the speed I swept the light. This emphasizes that the brightness is indeed not going to zero, just getting a lot dimmer, so this is not PWM. On the Fenix, it is clear that the light goes completely dark between cycles.


----------



## reppans

I get a similar thing with my D25A clicky on moonlight mode, but only with a low battery. However, I also have another copy that has this PWM-like behavior with fresh cells. Here's an old picture of it next to a Quark AAX... (FWIW, I have many LV head Quarks, and one HV, and have not noticed any PWM-like behavior.)


----------



## inetdog

FWIW, particularly in large LED replacements for incandescent in luminaires, the presence of a phosphor for CRI improvement can partially mask the PWM. The relaxation time of the phosphor can be greater than the period of the pulses.

Tapatalk...


----------



## Cataract

Great pics guys! I really like the idea of holding multiple lights together so you can have a fairly precise number on frequency based on a known one (provided you take the time to count all the bright spots)



inetdog said:


> FWIW, particularly in large LED replacements for incandescent in luminaires, the presence of a phosphor for CRI improvement can partially mask the PWM. The relaxation time of the phosphor can be greater than the period of the pulses.
> 
> Tapatalk...



Excellent to info. Never even thought of that.




Sent from somewhere in a tunnel, 42 minutes away from anywhere.


----------



## KARADENIZ

current-controlled, PWM  nice explained  thanks 
My Sipik SK68 is not CC or PWM, is it possible to update it ?


----------



## Cataract

KARADENIZ said:


> current-controlled, PWM  nice explained  thanks
> My Sipik SK68 is not CC or PWM, is it possible to update it ?



:welcome:

Thanks! I will add one or two things to the original post eventually, but for now I'm still unboxing stuff.

I'm not familiar with the Sipik as I don't own one or ever seen one in person. Try in the "homemade and modified flashlight" section; Almost every flashlight has been modified by someone at some point


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## KARADENIZ

hi 
everyday I learn something new  Flashlights are like Ecstasy 
I need PWM driver, is there any PWM driver comparison to their efficiency? price? and where to buy?

Edit: I've found this, is another greate post 
http://www.candlepowerforums.com/vb...ds-are-adapted-for-different-battery-voltages


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## Cataract

Great find there! I had to bookmark it, thanks.


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## flitter296

Cataract, thank you for this very informative post! Besides giving me a good understanding of what PWM is and why it is used, it helped me to understand why some of my flashlights have a much longer run time on low than others, when low is basically the same lumen rating with the same batteries.


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## Lord Muzzy

Great explanation! I had a general idea but this really clears things up. :goodjob:


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## Cataract

Thanks guys, I'm really glad I could put this clearly enough to help others. Comments like these really make me feel it was worth more than just the time I spent doing it


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## lmh0t3p

😄.w💩!#.!💩😋..w


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## Cataract

Erm... I don't know what's going on here... I thought this was a bot posting until I checked your other posts. Need any help?


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## Bullzeyebill

I'm interested too.

Bill


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## Louise1992

That is amazing . The light picture is a excellent description .That i would like to give it a try.


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## RI Chevy

Welcome to the Forum! :welcome:


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## xelario

"Your eyes are a little like tiny cameras that take about 24 pictures per second." This should be removed.


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## Cataract

xelario said:


> "Your eyes are a little like tiny cameras that take about 24 pictures per second." This should be removed.



It has been estimated that the _brain_ (yeah, not the eyes) processes about 24 frames per second. I'm not sure if there have been more recent studies into this, but the origin of this idea is that movies that showed less than 24 frames per second in the very debut of cinema made a lot of people regurgitate (to use the more polite way of saying what I have read). By experimenting, they had concluded that 24 frames per second kept the audience in their seat while keeping the length of reels as short (therefore less costly) as possible. 

This number is definitely debatable, but there is definite evidence that we cannot perceive more than a certain number of "pictures per second" if we compare to how movies are displayed on screen or on TV's or computer monitors. I did phrase it "a little like tiny cameras" and "about 24 frames per second" on purpose.


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## xelario

Cataract said:


> It has been estimated that the _brain_ (yeah, not the eyes) processes about 24 frames per second. I'm not sure if there have been more recent studies into this, but the origin of this idea is that movies that showed less than 24 frames per second in the very debut of cinema made a lot of people regurgitate (to use the more polite way of saying what I have read). By experimenting, they had concluded that 24 frames per second kept the audience in their seat while keeping the length of reels as short (therefore less costly) as possible.
> 
> This number is definitely debatable, but there is definite evidence that we cannot perceive more than a certain number of "pictures per second" if we compare to how movies are displayed on screen or on TV's or computer monitors. I did phrase it "a little like tiny cameras" and "about 24 frames per second" on purpose.



The brain can only process about 24 frames per second? Wow. I must be from a different species, then  In fact, a lot of people must be. I mean why else would we even have 120Hz monitors? And 144Hz? Madness! 
Why do TV movies at 30fps look different, than cinema 24fps ones? Why did people find The Hobbit's 48fps weird? Why even film and show it at 48 if 24 is all our brains can process? You talk about TV and movies, but never mention games. Maybe you're not a gamer. I am. If my eyes or brain only processed 24fps, I wouldn't have to buy expensive hardware to run games at >60, preferably >100. 30, 60, 100fps - there's a very noticeable difference to me.
In other words, it's a difficult subject, but neither our eyes nor brain are capped at 24 fps. That's why I think this claim should be removed. For someone who knows absolutely nothing about the subject reading this article would be highly misleading. The eyes don't "take pictures", they provide a continuos stream of data. The brain does not "take those images and assemble them into what we perceive as the continuous movie of our lives".
Please don't be offended, I hope it doesn't looks like I'm attacking you, I just don't like to see wrong or debatable data being presented as true fact and potentially misleading people in an otherwise good article.
If I were you, I'd drop the whole paragraph about 24 frames per second, it only adds to confusion. You explained it later: "The lower frequency PWM will be more perceivable to the eyes as a fast strobe effect – remember what it looks like to dance in a club when the only lighting around are strobes? Well, imagine that strobe is even faster, to the point that motion is almost continuous...".


----------



## WalkIntoTheLight

Around 24 fps is likely where our brains stop perceiving the images as individual pictures, and see them as fluid motion. That doesn't mean we can't perceive things faster than that, but it does seem to be a turning point of some kind. Stop-motion films at 12 fps do not look smooth at all. At 24 fps, we're willing to accept it as real motion.

My guess it probably has something to do with the amount of time it takes our brains to process an image from our optic nerves. If it takes more than 1/24s, then we just accept it as smooth motion.


----------



## xelario

WalkIntoTheLight said:


> Around 24 fps is likely where our brains stop perceiving the images as individual pictures, and see them as fluid motion. That doesn't mean we can't perceive things faster than that, but it does seem to be a turning point of some kind. Stop-motion films at 12 fps do not look smooth at all. At 24 fps, we're willing to accept it as real motion.
> 
> My guess it probably has something to do with the amount of time it takes our brains to process an image from our optic nerves. If it takes more than 1/24s, then we just accept it as smooth motion.



Again, "likely" is not "definitely". There is a lot to this subject. In the movies, the 24 frames per second look like fluid motion, but in games it doesn't. Because in movies fast motion is blured, while in games it isn't - the same goes with PWM, it's on or it's off. Try looking at a light at 24Hz - I did - it's visibly blinking. Also in the movies the 24 unique frames are not projected at only 24Hz, and so on. 24fps in the movies is not the same as a light at 24Hz PWM.
My point is, the whole 24fps thing in an article about PWM in flashlights is totally out of place and adds nothing usefull, no flashlight will use 24Hz or similar PWM. And the way it's written now is plain wrong and misleading.


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## Cataract

This is turning into a very interesting discussion that should be had on a completely different thread. Start that thread and I'll meet you there (PM me or link it here). The goal here is not to confuse people who want to learn about PWM.


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## xelario

Cataract said:


> The goal here is not to confuse people who want to learn about PWM.



And that's exactly what you're doing, IMHO... My goal here was not to start a discussion (so I won't start a new thread), but to remove the confusion. Finally you seem to understand, but only see the consequence (discussion) and not the cause (24fps paragraph). Maybe you don't think that text is confusing, misleading and/or wrong and is actually useful for people learning about PWM. Oh well, I did what I could


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## radiopej

Awesome. I always wondered what that picture people uploaded of a light trail meant.


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## Cataract

radiopej said:


> Awesome. I always wondered what that picture people uploaded of a light trail meant.





Jenifer512 said:


> Wow. Science is really fantastic. Thanks to all inventors behind this great LED improvement.



Thanks guys


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## radiopej

Thank you! I ran into the dark bathroom waving half of my lights right after reading. My girlfriend was very confused.


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## reppans

radiopej said:


> Thank you! I ran into the dark bathroom waving half of my lights right after reading. My girlfriend was very confused.



JMHO, but I wouldn't go looking for it :shrug:.

http://www.candlepowerforums.com/vb...to-detect-it&p=4307784&viewfull=1#post4307784


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## Cataract

LOL, but it's a great method to find a way to improve one's collection


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## feifei

well done, thanks for sharing the post,I have no idea about this,but have learnt a lot after reading the post.


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## Cataract

Thank you, it is really my pleasure to share the knowledge.


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## BrianHook

Nice work, I must say. Various points discussed here about LED flashlights are genuinely very informative.


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## Cataract

Thank you sir.


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## whiterabbit05

Thank you. I found this very useful when recently purchasing a Streamlight Protac HL and seeing PWM being mentioned in reviews of the light's low mode.


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## Cataract

Kinda sucks that Streamlight would go the PWM way. Were you able to detect it? Is it really annoying?


----------



## franksr

As a newbie to both LED lights and this forum I much appreciate your description of PWM as it has enlightened me and cleared up a few questions I had regarding PWM.


----------



## Cataract

franksr said:


> As a newbie to both LED lights and this forum I much appreciate your description of PWM as it has enlightened me and cleared up a few questions I had regarding PWM.



Thank you. There's nothing like knowing my article did what it was intended to


----------



## RI Chevy

This thread was one of the more informative and useful on this forum! :thumbsup:


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## Cataract

Whoa! Thanks a million! I definitely didn't expect that one


----------



## Neosec

Great job Cataract!!! :thumbsup:

Very well done and the photos really make the point. 

One thing I'll note that has changed (which doesn't matter much for the content of this topic) that you may or may not be aware of, you said:



> PWM is mainly used to control electric motors (like hybrid cars), but mostly step-motors like the ones in your hard-drive.



Hard drives (all?) no longer use stepper motors. The spindle motor is DC same as it's been and the armature motor is now a voice coil motor. Much faster.

Again, Great post!


Neo


----------



## Cataract

:thanks: AND :welcome:

Good to know about hard drives, I haven't been following computer technology evolution for a long while.


----------



## Mr. Tone

Cataract said:


> Kinda sucks that Streamlight would go the PWM way. Were you able to detect it? Is it really annoying?



My Streamlight has noticeable PWM on the medium and low modes.


----------



## Cataract

Mr. Tone said:


> My Streamlight has noticeable PWM on the medium and low modes.



Bummer. Thanks for sharing


----------



## RI Chevy

Mr. Tone said:


> My Streamlight has noticeable PWM on the medium and low modes.



Does it have the whine on the low modes as well? Or just the visual PWM? I really hate PWM!  I am a digital linear kinda guy!


----------



## Mr. Tone

RI Chevy said:


> Does it have the whine on the low modes as well? Or just the visual PWM? I really hate PWM!  I am a digital linear kinda guy!



I don't hear anything but it is visually obvious. That is an unfortunate design for an otherwise great LEO light.


----------



## bpierce

Great post. One question: is a circuit that supports higher frequency PWM more expensive to manufacture? Wondering why anybody would go with the lower frequency variety except maybe for cost reasons.


----------



## jorn

Some years ago i read that low frequency is more efficient. So i guess thats why. Dont know for sure, so dont quote me on that ;-)


----------



## Cataract

bpierce said:


> Great post. One question: is a circuit that supports higher frequency PWM more expensive to manufacture? Wondering why anybody would go with the lower frequency variety except maybe for cost reasons.



In general, higher frequency circuits are more expensive, so I would tend to say that is the reason for the tendency to use lower frequency circuits. 



jorn said:


> Some years ago i read that low frequency is more efficient. So i guess thats why. Dont know for sure, so dont quote me on that ;-)



I wouldn't quote myself either, but I think you're right, especially when it comes to a circuit that can drive an LED with higher amps.


----------



## Jvvjvv

I too would like to thank you for all the work you put into this thread. I too was unaware of PWM. It made me wonder that, if the differante way that the manufactures deliver the cycles, would cause a variance in battery drain?


----------



## Cataract

Jvvjvv said:


> I too would like to thank you for all the work you put into this thread. I too was unaware of PWM. It made me wonder that, if the differante way that the manufactures deliver the cycles, would cause a variance in battery drain?



I am starting to really feel humbled by all the thanks. Thank you all for your feedback 

The main goal of PWM is that it enables greater runtimes compared to constant current regulation. I have never really looked up the equations but, in theory, lower frequency PWM would mean longer runtimes since faster clocks generally need more energy. The difference in runtime VS PWM frequency might be fairly small and better quality chips can easily compensate for the difference in battery drain when using higher frequency PWM. The quality comes with a price as it does for everything else in life, though.


----------



## xzel87

I'm not sure how effective it is at various frequencies, but I can clearly see the PWM on my Lumintop Tool AAA on medium and low when I try to take a picture of the beam with my smartphone (HTC M7).It kinda appears as scan lines in the pic. Dropbox link below if anyone's interested.

https://www.dropbox.com/s/jp71zvwfzxsz7go/IMAG2661.jpg?dl=0

And, much thanks for the in depth information cataract.


----------



## Mr. Nobody

Is it possible for our brains or eyes to see PWM ? For example if I were watch a two people toss a football I am able to slow it down and perceive it as slow moving pictures. (Does that example make sense ?) Either I am weird or have a medical condition...either way I have lived with this for years and see a benefit.

This includes any moving object not just a football.


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## RI Chevy

Yes. We can see lights that have or use PWM.


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## reppans

Cataract said:


> *The main goal of PWM is that it enables greater runtimes compared to constant current regulation*. I have never really looked up the equations but, in theory, lower frequency PWM would mean longer runtimes since faster clocks generally need more energy. The difference in runtime VS PWM frequency might be fairly small and better quality chips can easily compensate for the difference in battery drain when using higher frequency PWM. The quality comes with a price as it does for everything else in life, though.



Interesting, HKJ mentioned that current regulated lights should be more efficient. However, I do output/runtime tests on the sub-/low- lumen modes I use most often and find it all over the map... so - clear as mud .

http://lygte-info.dk/info/DriverTypes UK.html


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## scs

Pwm bothers me when its frequency is low enough that I can detect it by waving my hand very rapidly in front of the light ,and my hand appears to fan out like a deck of cards in hand.


----------



## Cataract

reppans said:


> Interesting, HKJ mentioned that current regulated lights should be more efficient. However, I do output/runtime tests on the sub-/low- lumen modes I use most often and find it all over the map... so - clear as mud .
> 
> http://lygte-info.dk/info/DriverTypes UK.html



Hmm... I might have been a little tired when I wrote that and failed to elaborate properly as it is possible to achieve longer runtimes with PWM _under certain conditions_. I prefer to keep things simple in this thread as it is intended to be easy to understand for everyone. Each has its advantages when it comes to runtime. For those who wish to study further, that link is an excellent read. Thanks for the link.




scs said:


> Pwm bothers me when its frequency is low enough that I can detect it by waving my hand very rapidly in front of the light ,and my hand appears to fan out like a deck of cards in hand.



I know exactly what you mean. I once tried to walk fast in an overgrown field while using a PWM headlamp. All the moving blades of grass looked like they multiplied and went slow-mo on me. ARGH!


----------



## shanewang

nice thread, really helpful for beginners like me


----------



## jon_slider

I recently started looking at single aaa lights and was interested in the Rev3 Maratac Cu, but am concerned about the PWM.. anyone care to comment whether they think the Maratac has good or bad PWM on any brightness setting?

here is my cheat sheet, hopefully accurate
==

includes hat clip, and No PWM


Olight i3s 20-85-0.50 lumens in mode sequence XP-G2 
Thrunite Ti3 Aluminum 0.04-12-120 XP-G2
Thrunite Ti3 Stainless 0.04-12-120 XP-G2
Thrunite Ti3 Titanium 0.04-12-162 XP-L4 (Very floody and green compared to G2)


no hat clip, and No PWM
Fenix E05 2014 Aluminum 8-25-85 XP-E2 (more blue than G2)
Fenix E05 2014 Stainless 8-25-100 XP-E2
Fenix E05 2014 Titanium 4-27-100 XP-E2

===
===
Lighs with PWM and hat clip


Maratac Rev3, 40-1.5-138 XP-G2
ITP A3 1.5-18-80 XP-G2
===


----------



## Flyingdrums

Long time reader first time poster. I was on a search to put together my own PWM circuit for the high power LED light's that I build and finally settled on one based around the 555 timer (basically because I had all the components on hand). I hope to start a thread with it when I get my required posts because I try to include a little "light" hearted humor that hopefully people interested in this sort of thing can enjoy. Here is a link to the video that contains the circuit diagram used. No commercials, I promise.


----------



## Cataract

@ ion_slider: thanks for sharing that info.

@ Flyingdrums: That's a crazy build and gotta love that intro  Your video would likely get better deserved attention in the homemade and modified flashlights section, though.


----------



## RI Chevy

Welcome to the forum! :welcome:


----------



## Flyingdrums

Thanks! I'll post it there when I get the all clear for starting a thread.


----------



## Cataract

You're only a few posts away....

Yea, I completely forgot :welcome:


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## jon_slider

another copper aaa light with PWM, but no hat clip is the Prometheus Beta, discussed here:
http://www.candlepowerforums.com/vb...-QR-LIVE-on-Kickstarter&p=4641643#post4641643


gunga said:


> I notice the pwm. It's not bad but
> I can notice it.





neutralwhite said:


> Same.



Im expecting delivery of a Rev3 maratac, will share my PWM impressions shortly.


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## hbk_rey

I like the copper AAA.


----------



## jon_slider

I have not been able to detect the PWM when using my recently arrived Maratac, unless I shine the light at a fan or running water. My phone camera does not pick it up. Im really liking the copper body. First impressions and pic links here http://www.candlepowerforums.com/vb/showthread.php?400559


----------



## AHRS-24/7

Thank you for this......good start for a new flashlight nerd.


----------



## masterP

is it mostly cheaper offshore brands that use PWM? I never even heard of it until I read it here

can you list what brands use PWM? I guess it doesn't apply to flashlights that only have one mode.....just the ones with about 4 or 5 different brightness levels? what about other regulated LED's? someone said they think a Malkoff is PWM.....do you really think a high end light is going to be PWM?

also some people said they get dizzy or nauseous when they're driving behind a Cadillac or a Volvo. now I'm gonna be looking for Cadillacs and Volvo's to see what they mean

does this affect everyone or just some people?

this just made me think twice about buying anything FourSevens or Fenix......or anything that has multiple brightness levels. or anything regulated

how do you know which ones are and which ones aren't? I don't want to buy anything that's gonna make me nauseous or anyone else. I don't even like strobe lights, they make everyone disoriented and dizzy.....I think this is a bad idea if you think it's a good way to defend yourself from an attacker. kind of like bear spray....not only is the bear gonna be choking on it.....so will you


----------



## jon_slider

Lights are either PWM or current regulated. The specs disclose it. 

Im new, and only have single aaa experience. 
Maratac Rev 3 uses PWM. This gives it nice color. 
Olight I3s has just as good color, and has no Pwm. I recommend the olight. 
thrunite Titanium has no pwm, but terrible green color. 
Fenix e05 2014 model has no PWM. The color is a bit blue. I like the light, the threads are smooth operating, but has no pocket clip. 

Dont avoid multi level, that's not a determinant of PWM


----------



## Cataract

masterP said:


> is it mostly cheaper offshore brands that use PWM? I never even heard of it until I read it here
> 
> can you list what brands use PWM? I guess it doesn't apply to flashlights that only have one mode.....just the ones with about 4 or 5 different brightness levels? what about other regulated LED's? someone said they think a Malkoff is PWM.....do you really think a high end light is going to be PWM?
> 
> also some people said they get dizzy or nauseous when they're driving behind a Cadillac or a Volvo. now I'm gonna be looking for Cadillacs and Volvo's to see what they mean
> 
> does this affect everyone or just some people?
> 
> this just made me think twice about buying anything FourSevens or Fenix......or anything that has multiple brightness levels. or anything regulated
> 
> how do you know which ones are and which ones aren't? I don't want to buy anything that's gonna make me nauseous or anyone else. I don't even like strobe lights, they make everyone disoriented and dizzy.....I think this is a bad idea if you think it's a good way to defend yourself from an attacker. kind of like bear spray....not only is the bear gonna be choking on it.....so will you



1- Yes and no. Most cheaper brands use slower PWM regulation. Some higher priced brands do use PWM regulation, but the frequency is high enough that it is very hard or even impossible to detect.

2- I don't have a list of brands, but I do invite people to list them here. If I had more time, I would compile the list myself but if someone else is willing to do it, I would gladly include that list in my first post of this thread.

3- I have never seen a single mode flashlight that uses PWM, but it still could exist.

4- As mentioned above, most high end lights avoid PWM but, when they do, it is usually with a frequency that is hard to detect. I have some high end lights that use PWM and they don't bother me one bit, while the cheaper, lower frequency ones, bother me greatly.

5- I once had to slow down because the Cadillac in front of me had such low frequency PWM my eyes couldn't focus. I think they made some changes as the newer models do not bother me one bit. Some people are very sensitive to PWM, some are not at all. That can also be relative to the frequency used in the PWM (lower frequency is worse).

6- Foursevens and Fenix are fine as farr as I know. Most multiple level lights are fine by now, but you can ask around or read reviews before buying a light. 

7- I explained in my first post how to detect PWM. Mostly, if your light doesn't bother you and does what is was intended to, it should be a good light for you.




jon_slider said:


> Lights are either PWM or current regulated. The specs disclose it.
> 
> Im new, and only have single aaa experience.
> Maratac Rev 3 uses PWM. This gives it nice color.
> Olight I3s has just as good color, and has no Pwm. I recommend the olight.
> thrunite Titanium has no pwm, but terrible green color.
> Fenix e05 2014 model has no PWM. The color is a bit blue. I like the light, the threads are smooth operating, but has no pocket clip.
> 
> Dont avoid multi level, that's not a determinant of PWM



Thanks jon!


----------



## masterP

thanks for answering all my questions....sometimes I think it'd be better off being ignorant, then I wouldn't be thinking about PWM all the time

before reading this thread I would never have known anything about it but I have OCD so now it's always in my mind


----------



## Cataract

masterP said:


> thanks for answering all my questions....sometimes I think it'd be better off being ignorant, then I wouldn't be thinking about PWM all the time
> 
> before reading this thread I would never have known anything about it but I have OCD so now it's always in my mind



NP dude, that's what I started this thread for.

I like to think about martial arts (and therefore just about any knowledge) this way: when you know nothing, you have no idea what danger is. When you know little, you can be a danger to yourself and others. When you master enough knowledge, you can defend yourself in any situation without making anyone a vegetable or a cripple. 

Mastery is the key. Learn on your passion and make everyone else's life safer.


----------



## jon_slider

single aaa 

Lights with PWM
iluminatiiTP A3PrometheusBetamaratac Rev3
Lights with Current Regulation

fenix e05fenix e01fenix ti99
Fenix LD01
Olight i3s
Thrunite Ti3


----------



## Hondo

Need to move the Fenix LD01 up. Definitely has PWM, although at a decently high frequency. Waving it back and forth generates a clear dotted line of light.

e01 does not have PWM, but it's a single level light, which would never have it. The purpose of PWM is to provide a lower level than 100% on cycle, by pulsing the full brightness for a perceived lower level.


----------



## jon_slider

Hondo said:


> Need to move the Fenix LD01 up. Definitely has PWM



I think that was true of older models, but they are now current regulated instead of pulse width modulated afaict
http://www.candlepowerforums.com/vb...nix-LD01-current-regulated-now-or-only-the-SS


Ice said:


> I took the risk and ordered an LD01 with an R4 LED (which made me believe it had to be rather new).
> And to my delight the light seems to be current regulated, there's no PWM visible (very much in contrast to the older LD01)!!!
> 
> So if you get an LD01 with an R4 LED I would bet it is current regulated!


----------



## masterP

I'm gonna stick to single level lights. they wouldn't be PWM would they? even if they were regulated?

what about Surefire? are they PWM?

do some lights use CC and PWM together? is it mostly the moonlight mode and lowest light setting that use PWM?


----------



## Hondo

Hmm... Looks like a running change. I checked my older SS XR-E model LD01 which has it, but then I checked my more recent SS XP-G model from about a year ago, and it does not appear to have PWM. So new product looks like current regulated. All way better than the 100 Hz L0D.


----------



## jon_slider

masterP said:


> what about Surefire? are they PWM?
> http://www.surefire.com/illumination/flashlights/titan-a.html


Features​
Virtually indestructible, high-performance LED is regulated to maximize output and runtime



masterP said:


> ...is it mostly the moonlight mode and lowest light setting that use PWM?



Surefire Titan has no PWM, 2 modes, this sequence, 15-125

If you dont want moonlight, dont want PWM, and dont want a pocket clip, get the excellent Fenix E05 2014 edition. The lumen sequence is 8-25-85. It has very nice smooth threads for one hand operation.

If you do want moonlight, still no PWM, and do want a reversible pocket clip, and will learn to love a M-H-L sequence, I recommend the Olight i3s. Its sequence is 20-85-0.5, it also has super smooth threads, works great one handed.

Note that you can just turn on the 1st mode if you dont want multimode , and still grow into the other modes 

You can also determine if PWM is present by shining a light you buy on a stream of water, a shower, or a spinning fan.

I did that with my Maratac Rev3 after I could not detect the PWM with my phone camera. 

Yes youre understanding correcly that PWM is used on all but the highest level. The advantage of PWM is the LED is Pulsed at full power and gives full color. PWM is not necessarily bad, I was swayed by the comment that some people refer to PWM as Constant Color, so I went ahead with my purchase of a Maratac Rev 3 even knowing it had PWM. Honestly, I cant tell and I like the light. Sometimes when Im making buying decisions, I focus on things that end up becoming less important to me in practice.

Anyway, it is easy to avoid PWM, even in multi mode lights. Pick one you like and post a review 



Hondo said:


> Hmm... Looks like a running change. I checked my older SS XR-E model LD01 which has it, but then I checked my more recent SS XP-G model from about a year ago, and it does not appear to have PWM. So new product looks like current regulated. All way better than the 100 Hz L0D.



Agree. Curious what technique you find convenient when checking for PWM?


----------



## masterP

what about the Fenix E15 and Fenix PD35 2014 edition? any PWM?


----------



## jon_slider

masterP said:


> what about the Fenix E15 and Fenix PD35 2014 edition? any PWM?



start by reading the descriptions. Look for the words Pulse Width Modulation (PWM), versus Digitally Regulated Current.

here, I found the links you need to start with
http://www.amazon.com/dp/B005CWRB44/?tag=cpf0b6-20

http://www.amazon.com/dp/B00JK5Y1NS/?tag=cpf0b6-20

Come back after you do your research and tell us if those two lights have PWM. This is a test to see if you have learned how to answer your question.

You can also write Fenix directly to ask your questions. Please share what you learn.

I would rather teach you how to fish, than have you use this sticky thread to ask a series of what to buy questions. That is best done in a new thread of your own.


----------



## masterP

I have emailed surefire about their lights.....no answer yet

I have never seen anyone advertise their flashlights as using PWM......I don't think it's something they would want to brag about

I thought digitally regulated current applies to both current controlled and PWM

I will email Fenix and report back.....and Foursevens 










jon_slider said:


> start by reading the descriptions. Look for the words Pulse Width Modulation (PWM), versus Digitally Regulated Current.
> 
> here, I found the links you need to start with
> http://www.amazon.com/dp/B005CWRB44/?tag=cpf0b6-20
> 
> http://www.amazon.com/dp/B00JK5Y1NS/?tag=cpf0b6-20
> 
> Come back after you do your research and tell us if those two lights have PWM. This is a test to see if you have learned how to answer your question.
> 
> You can also write Fenix directly to ask your questions. Please share what you learn.
> 
> I would rather teach you how to fish, than have you use this sticky thread to ask a series of what to buy questions. That is best done in a new thread of your own.


----------



## Hondo

masterP said:


> I thought digitally regulated current applies to both current controlled and PWM




I believe this is a true statement.

As for how I check for PWM, I hold the light in front of me at an angle, so it is not pointing directly in my eyes, but I can see the reflector, so my eyes are probably at the edge of the spill. Then I wave the light up and down as fast as I can, and look for the dotted line of light. Close dots for high frequency PWM, wide dots for low frequency PWM (yuck!). If you look at my post #115 you can see a photo I took of this, showing both cases as well as a Quark that is not technically PWM, as it does not go all the way dark at the low cycle, but it looks just like PWM in use. Looks like it is pulsing in a sinusoidal fashion, what has been called "circuit warble". A light without PWM will show a smooth streak of light.


----------



## jon_slider

masterP said:


> I have emailed surefire about their lights.....no answer yet
> 
> I have never seen anyone advertise their flashlights as using PWM......I don't think it's something they would want to brag about
> 
> I thought digitally regulated current applies to both current controlled and PWM
> 
> I will email Fenix and report back.....and Foursevens



fair enough, you definitely are doing your homework. I will offer my opinion, as a consumer, not an expert. My understanding is the two Fenix lights you asked about are Regulated. To me that means no PWM.

The Prometheus Beta is PWM with a Nichia 219 led. They are serious about color rendition, so PWM is the choice since it fires the LED at full power, albeit as a strobe. PWM is also present in the Rev3 Maratac. These are not cheap lights. The decision to avoid PWM does not really limit your choices. Like you I was at first totally turned off to PWM. But I do not think it is necessarily a deal breaker. The use of PWM is a benefit, if you want good color on some of the lower light levels.

I agree both Prometheus and Maratac do not disclose they use PWM. I find that info by googling the name of the light with keyword PWM. That pulls up lots of links that discuss whether those lights use PWM or not.

for example "Fenix E15 PWM" search result:
http://www.candlepowerforums.com/vb...ncerns-I-ve-read-on-CPF-about-this-little-gem
"*It is not PWM.*"​another google search example "Fenix PD35 2014 PWM" search result:
http://www.candlepowerforums.com/vb...0-Lm-powerful-compact-18650-flashlight-REVIEW
"*The brightness is current controlled,so there's no any sign of pwm.*"

Happy Shopping! share what you end up with and how you like it.


masterP said:


> I thought digitally regulated current applies to both current controlled and PWM





Hondo said:


> I believe this is a true statement.


I respectfully disagree, but am open to learning. To me the word Regulated means Current Regulation, not Pulse Modulation. I do not think they are the same, but welcome links to educate me better. I agree it is unclear in the Fenix literature, which is why I google for confirmation.


----------



## hiuintahs

jon_slider said:


> .................To me the word Regulated means Current Regulation, not Pulse Modulation. I do not think they are the same, but welcome links to educate me better.


 Yes. "Regulation" in the electronics field means constant output (non-varying). Therefore PWM (pulse width modulation) is not a regulated output......but a varying output. A regulated output that holds a constant output requires a feedback signal. PWM does not. That is the advantage of PWM is that the driver is more simple. But the tradeoff is that its also less efficient. Now a PWM driven LED will look like a constant brightness but the voltage across the LED and the current through it are not regulated but do have an average value per cycle and that makes it look constant .


----------



## Cataract

As far as I can tell, to this day, Fenix and Foursevens are completely avoiding PWM in their lights. The only Fenix I know that used PWM wad the L0D, which has been replaced by the LD01 and LD02, which are now CURRENT regulated. 

Hondo is right, "digitally regulated" could mean current regulated or PWM regulated. "Digitally regulated" only means that a digital chip is taking care of the regulation and the output intensity will be constant, but that does not tell in which way the output regulation is implemented.

If you read between the lines, the statement you are ideally looking for is "current regulated", not just "digitally regulated". Unfortunately, that specific description is not used often enough and one seller could mention it while others might not. That is why I most often check out the manufacturer's website for the most complete description and sometimes even have to check out multiple resellers if I can't find a good review. You still might have to ask around for a definitive answer after all that work, though.

Selfbuilt would be the biggest authority on electronics testing and I do recommend to check out his LD02 review as a first homework on regulation, which might help you understand why Fenix is such a legend when it comes to current regulation and perhaps dissipate fears on flashlights that are made in China.


----------



## jon_slider

We agree the current Fenix are Current Regulated, not PWM. 
imnsho Digitally Regulated means not PWM also. The term Regulated is used by Fenix to distinguish from PWM, that they used to use.

two examples:
http://edcforums.com/threads/fenix-l0d-vs-ld01.87963/
"The very best improvement on the LD01 vs L0D is the faster PWM rate and now the newest version use constant current regulation. The L0D was using a very slow PWM rate that is among the most annoying low levels I've ever seen. It now uses a digital regulation for non-strobing lower levels."

http://www.candlepowerforums.com/vb/showthread.php?400630-Fenix-LD02-(XP-E2-1x-AAA-clicky)-keychain-review-RUNTIMES-BEAMSHOTS-and-more
"Digitally regulated output - maintains constant brightness"
"*No PWM*
There is no sign of pulse width modulation (PWM) at any output level on LD02 - the light appears to be fully current-controlled and flicker-free. "

---
imho these terms are interchangeable:
Regulated = Constant Current = Current Controlled = Digital Regulation = Constant Brightness

and all of the above are different than:
PWM = Pulse Width Modulation = Constant Color


----------



## Hondo

At least "back in the day", regulated meant the ability to achieve near constant brightness. Using NiMH batteries can give this effect due to the discharge nature of the battery, but alkaline batteries in an unregulated light will give a long, concave declining discharge curve. If you look at Selfbuilts runtime chart for the L0D, particularly the alkaline curve, you will see that it is doing a very good job of holding brightness to the end with a battery that hates giving out constant power, yet the light achieves the same characteristic curve as it does with the NiMH battery. In my book, that sucker is well regulated. And it is also the king of PWM at the same time.








Now this is an unregulated light, look at the Saphire and Tikka (Quickbeam's plots):


----------



## jon_slider

The Tikka is a PWM light. You call it unregulated. I find that confusing only when you call the LOD regulated and PWM in the same breath.

anyway, when Fenix says digitally regulated now, they mean no PWM, I think we can agree.

Note the use of pwm as opposed to current controlled regulation in this self built review:
*http://www.candlepowerforums.com/vb/showthread.php?321587*
*"No PWM/Strobe*
Here’s a nice find – there is no sign of PWM on the Lo mode of the Worm. 




 It thus seems to use current-control for its low mode.
…
Current-controlled circuit performance is excellent – very flat regulation, and top-of-class runtimes at both levels."


----------



## Cataract

jon_slider said:


> The Tikka is a PWM light. You call it unregulated. I find that confusing only when you call the LOD regulated and PWM in the same breath.
> 
> anyway, when Fenix says digitally regulated *now*, they mean no PWM, I think we can agree.



Let me clarify things a bit for you. I believe your confusion is coming from the fact hat 2 concepts are intermingled here, something I did not quite realize when I started this thread. 

There are 2 concepts that should be distinguished from each other, namely "output regulation" and "mode regulation".

"Output regulation", short for "Constant output regulation", means the number of lumens coming out from the LED should be constant over a period of time until the battery(ies) can no longer give out enough energy to maintain the selected output. 

"Mode regulation" or "mode control" do not necessarily mean that the lumens output will trace an exact flat line over time. Mode regulation can be achieved through current control (sucking a proportional number of amps from the battery to feed the LED the appropriate number of amps for a specific output) or through PWM (it is simpler to send you back to my first post graphs than to elaborate again on this one.) In theory, current control should give a very constant result like a flat line (if we ignore varying qualities in circuitry). 

PWM alone does not mean the output will be constant in intensity; PWM switches the LED on and off at maximum achievable power with various on-to-off ratios for each mode (on for less time and off for more time to achieve lower modes; just refer to the graphs in my original post). If the manufacturer did not include circuitry to compensate the fact that batteries lose power as they discharge, you can have a PWM light that does not have a constant output since the maximum output power will diminish over time. AFAIK, PWM controlled lights pretty much all include some form of output regulation - else I doubt they would still sell their lights. However, since the entire goal of PWM is simplicity and cheapness of the circuits, most PWM controlled lights have less-than-ideal output regulation circuits.


Let me know if this explanation clears things up for you and which part is not clear enough. I'll be glad to help and this would also help me update my original post to make things as clear as possible for Mr. everybody. I'm also open to hear from other experts to correct me if I made a mistake. I'm not looking into making a Wikipedia-worthy entry, just a good description that can be understood by the Mr. Everybodies out there.


----------



## masterP

the foursevens mini 123 is PWM

http://www.laymanslights.venturous.org/blog/2010/01/4sevens-q-mini-123/


----------



## masterP

my email response from Fenix.....



Dear customer,

Thank you for supporting Fenix.

Fenix products are Current Control reglated.

Best regards.
 
Linda Yao
Fenixlight Limited 
8/F, 2nd Building,
DongFangMing Industrial Center
33rd District, Bao'an,ShenZhen 518133 China
0086-400 886 6093
www.fenixlight.com
www.facebook.com/fenixproducts


----------



## Hondo

jon_slider said:


> The Tikka is a PWM light. You call it unregulated. I find that confusing only when you call the LOD regulated and PWM in the same breath.




Thanks Cataract for the detailed explanation. I was just going to say that use of PWM to control brightness levels does not ensure regulation of brightness throughout the discharge of the battery. It does not preclude it either, the above two lights are an example of both conditions. And while I don't have an example I can think of, I am sure it is possible to control brightness with a current controlled circuit and fail at achieving flat regulation as well.


----------



## jon_slider

masterP said:


> the foursevens mini 123 is PWM
> 
> http://www.laymanslights.venturous.org/blog/2010/01/4sevens-q-mini-123/



Total respect for your research and for providing a link as supporting evidence.



masterP said:


> Fenix products are *Current Control reglated*.



Well researched! Clearly the word Regulated as used by Fenix means Current Controlled, not Pulse Width Modulated.


----------



## reppans

I agree with Cataract and Hondo... PWM vs Current Control and Regulated vs Unregulated are independent of each other, you can have all four combinations. Two examples of current controlled, yet unregulated, are the ET D25A and 47 Atom on moonlight mode - both outputs will vary ~5x depending upon voltage (ie, new 1.7v L91 to dead 1.2v NiMh). My Malkoff MDC AA is PWM light, and it's moonlight mode also displays the same voltage sensitive, although it's other modes seem well regulated. 

Some may actually claim all CC, but still have some PWM, like this ET D25A on 3lms on the left. On the right is a 47s Mini (PWM is spec'd) - these are the two fastest PWM lights I've seen - this sweep is as fast as I can move my arm. 






Btw, 47s uses PWM across the Mini line and Preon P1 and P2, but otherwise is CC AFAIK (although I know Hondo has, and certain other early samples I've seen, Quarks with PWM warble effect). I have quite a few (I suppose later model) Quarks and they are all nicely CC and well regulated. My D25A also has that warble effect on moonlight at low V, pics posted earlier in this thread. 

Don't own any Fenix lights, but the definitive way to tell is a fast sweep across a DSLR on time exposure, side-by-side with a known fast PWM light, and a true CC light (as above). My own eye-ball detection method is catch the spill in a reflection/mirror and move my eyeballs left to right quickly - I can quite easily see the PWM on the 47s Mini, but it is very hard to detect it on the D25A.


----------



## hiuintahs

Hondo said:


> ............I don't have an example I can think of, I am sure it is possible to control brightness with a current controlled circuit and fail at achieving flat regulation as well.


Well, not entirely true if designed properly. The nature of LED's is that their output is constant per current at a given junction temperature



.

Current controlled is sensing the current through the LED and translating that into a voltage feedback signal back into the driver that then regulates or holds the Vf across the LED such that it holds a constant current. Light output will be pretty flat with a slightly down slope as the junction temperature of the LED heats up. It all depends on how hard the LED is being driven. Low and medium modes will be very flat over time if done right.

As I have seen some reiterate, the confusion that I see is that the term "regulated" means constant output. That can be constant voltage or constant current as in ideal power supplies or constant brightness as in the output of an LED. If the circuit is regulated, then there is a feedback signal to the driver. The problem with PWM is that unless, the circuit compensates by increasing the duty cycle of the pulse width as the battery voltage drops, you will see the output drop with depletion of the battery. Constant light output in a PWM system would require feedback of some type and more complexity thereby defeating the simplicity of PWM........then might as well go with current controlled.

To me I don't care how they derive the driver, the winner is the one with the most efficient and flat line output over the time the battery discharges. Once I got a data logging light meter, built a light box patterned after Selfbuilts, this hobby took on new meaning as not all lights are created equal.


----------



## Cataract

Hondo said:


> Thanks Cataract for the detailed explanation. I was just going to say that use of PWM to control brightness levels does not ensure regulation of brightness throughout the discharge of the battery. It does not preclude it either, the above two lights are an example of both conditions. And while I don't have an example I can think of, *I am sure it is possible to control brightness with a current controlled circuit and fail at achieving flat regulation as well*.



1- As far as I can tell, good manufacturers that use PWM for mode control, also include some form of output regulation. How they perform on output regulation does depend on the quality of the circuitry. Some are so bad the output curve pretty much parallels a battery output curve and it would only be normal to question if the even try to keep the output constant.

2- *Most fail to achieve absolute flat output regulation with current control* to varying degrees; it is a very tricky thing to come up with an absolute flat line like Fenix does (just check out Selfbuilt's collection of output graphs). That said, I don't really mind if a light can give me at least ~75-80% flat output regulation since I will probably not notice it even if I try hard. Sometimes other factors are more important that a brick solid output intensity.




reppans said:


> I agree with Cataract and Hondo... PWM vs Current Control and Regulated vs Unregulated are independent of each other, you can have all four combinations. Two examples of current controlled, yet unregulated, are the ET D25A and 47 Atom on moonlight mode - both outputs will vary ~5x depending upon voltage (ie, new 1.7v L91 to dead 1.2v NiMh). My Malkoff MDC AA is PWM light, and it's moonlight mode also displays the same voltage sensitive, although it's other modes seem well regulated.
> 
> Some may actually claim all CC, but still have some PWM, like this ET D25A on 3lms on the left. On the right is a 47s Mini (PWM is spec'd) - these are the two fastest PWM lights I've seen - this sweep is as fast as I can move my arm.
> 
> 
> 
> 
> 
> 
> Btw, 47s uses PWM across the Mini line and Preon P1 and P2, but otherwise is CC AFAIK (although I know Hondo has, and certain other early samples I've seen, Quarks with PWM warble effect). I have quite a few (I suppose later model) Quarks and they are all nicely CC and well regulated. My D25A also has that warble effect on moonlight at low V, pics posted earlier in this thread.
> 
> Don't own any Fenix lights, but the definitive way to tell is a fast sweep across a DSLR on time exposure, side-by-side with a known fast PWM light, and a true CC light (as above). My own eye-ball detection method is catch the spill in a reflection/mirror and move my eyeballs left to right quickly - I can quite easily see the PWM on the 47s Mini, but it is very hard to detect it on the D25A.



I found a very old post from 47's (before the mini line) that stated they did not use PWM in their lights, despite the light showing signs of it when you move it as fast as you can. They said that this is actually an artefact from the circuits used. When viewing a graph of the current output at the LED, it became obvious that the time on - time off proportions never changes, but there was a small dip at regular intervals on the graph. In a sense, it is not actual PWM, but does behave somewhat the same (it should be much, MUCH easier to detect on lower modes, but isn't really that much easier to detect). The frequency of that dip is very high though, and it is hard to find as you must have experienced yourself. I don't know if the same really applies to the quark mini line, but I can say that none of my quarks bother me with signs of PWM and I have not heard from anyone saying it does. It does look the same and I thought it was actual PWM until I read their post. Now I give them the benefit of the doubt.


----------



## Cataract

hiuintahs said:


> *Well, not entirely true if designed properly*. The nature of LED's is that their output is constant per current at a given junction temperature .
> 
> Current controlled is sensing the current through the LED and translating that into a voltage feedback signal back into the driver that then regulates or holds the Vf across the LED such that it holds a constant current. Light output will be pretty flat with a slightly down slope as the junction temperature of the LED heats up. It all depends on how hard the LED is being driven. Low and medium modes will be very flat over time if done right.
> 
> As I have seen some reiterate, the confusion that I see is that the term "regulated" means constant output. That can be constant voltage or constant current as in ideal power supplies or constant brightness as in the output of an LED. If the circuit is regulated, then there is a feedback signal to the driver. The problem with PWM is that unless, the circuit compensates by increasing the duty cycle of the pulse width as the battery voltage drops, you will see the output drop with depletion of the battery. Constant light output in a PWM system would require feedback of some type and more complexity thereby defeating the simplicity of PWM........then might as well go with current controlled.
> 
> To me I don't care how they derive the driver, the winner is the one with the most efficient and flat line output over the time the battery discharges. Once I got a data logging light meter, built a light box patterned after Selfbuilts, this hobby took on new meaning as not all lights are created equal.




A "slightly" more advanced detailed explanation than I meant to see here when starting the thread, but very well explained (at least, for those who can follow). The feedback loop is what creates that small high frequency dip on the Quarks output IIRC. I might have learned a thing or two from your post...

Your post started with the answer to the riddle: circuit quality differs and some (most, really) fail to achieve absolute flat output and my belief is that has more to do with not being able to completely compensate for the battery discharge state since that is the core of the challenge (but I could be wrong). Different reasons could help explain this: not enough research, trying to keep the cost down, trying to minimize the size of the driver, etc. I think others might also just go with the flow so they can state longer runtimes on the box.

I think "output regulation" or "regulated" are, in general, used by manufacturers to mean that the average output intensity is better than just connecting the battery(ies) straight to the LED and I wouldn't say it is a deception in itself to claim so; they did do _something_. I'm not arguing that flat output isn't ideal, but the word "regulation" as used in the industry IMO simply means that circuitry was used to give a more constant output than doing nothing. Some are just so much better than others at it and can simply stand on their reputations without needing to flip backwards to explain it in more details than it should be needed to. I still do love my less-than-ideal current controlled lights so long as I don't notice the difference as I'm using them


----------



## jon_slider

I was unable to detect the PWM of my Maratac Rev 3 by waving the light, video, or still photo. However I can see the PWM strobe effect very slightly on a fan, or on running water.

some discussion that includes the Constant Color benefits of PWM
http://www.candlepowerforums.com/vb/showthread.php?331102-Please-comment-Quark-Mini-AA-quot-PWM-quot


calipsoii said:


> The Quark's use a very high frequency PWM - it's extraordinarily unlikely that your eyes will notice that it's there.
> 
> On a HCRI light like the one you purchased, you should be grateful that the levels are PWM-controlled. Constant current drivers cause noticeable tint shift as you decrease the output, meaning you might get an ugly orange instead of a creamy white. Any PWM-generated levels will have the same tint as full brightness.





calipsoii said:


> Probably, though the amount of shift varies by each emitter so you might wind up with a model where it's not even noticeable. It's pretty random, but I don't like rolling the dice on whether it turns green at a low setting.
> 
> I'm personally of the opinion that if I'm buying a light for it's premium tint (like a HCRI) then I want that tint at all levels, even if it means losing some runtime. McGizmo's Sundrop or HCRI Haiku is a good example of a light where I'm glad he went with a PWM driver.



The Prometheus Beta Copper, which has a N219 and a low of 1 lumen, also uses PWM.

Just playing devils advocate so we can be aware that not all PWM is slow, bad, or limited to cheap lights.. PWM has benefits in terms of color fidelity on low levels.


----------



## reppans

To avoid confusion, 47s separated the Quark line from the Mini line - earlier on the Mini was called "Quark Mini." 47s does specify "PMW" for the Mini, and "Current Regulation" for the Quarks on its website. 



Cataract said:


> I found a very old post from 47's (before the mini line) that stated they did not use PWM in their lights, despite the light showing signs of it when you move it as fast as you can. They said that this is actually an artefact from the circuits used. When viewing a graph of the current output at the LED, it became obvious that the time on - time off proportions never changes, but there was a small dip at regular intervals on the graph. In a sense, it is not actual PWM, but does behave somewhat the same (it should be much, MUCH easier to detect on lower modes, but isn't really that much easier to detect). The frequency of that dip is very high though, and it is hard to find as you must have experienced yourself. I don't know if the same really applies to the quark mini line, but I can say that none of my quarks bother me with signs of PWM and I have not heard from anyone saying it does. It does look the same and I thought it was actual PWM until I read their post. Now I give them the benefit of the doubt.



All my later model Quarks are very smooth (and have very flat output "regulation," aside from Max), and I love them, but I bought a used Titanium 123^2 (circa 2010 or 11?) that has very noticeable PWM-like behavior (or artifacts). Haven't take a picture of it yet, but I suspect it's the same as what Hondo posted here (post #115) and what Ti-force posted here (I posted smooth samples):

http://www.candlepowerforums.com/vb...Quark-Tactical-QT2L-X-Burst-Mode-review/page3


----------



## reppans

jon_slider said:


> .... PWM has benefits in terms of color fidelity on low levels.



I know this is conventional wisdom but don't see the current regulation tint shift thing. This is an old photo of some lights on moonlight (top) and something around 100 lms (bottom) - camera is on auto white balance and auto exposure (-2? exposure comp) for both - can anyone tell which are current regulated and which are PWM? 






I also wonder about current regulation efficiency thing too.. I test my lights for output and runtime on the sub-/low-lumen modes I use most (with a lightbox). My PWM Malkoff MDC AA tested about double the lumen-hours on moonlight mode vs a bunch of current regulated lights in a side-by-side test (note though, the MDC is not particularly well "temperature regulated" ).


----------



## Cataract

Thanks for the info. I can understand they wanted to keep it simple early on and I definitely am not bothered by PWM on my mini's. I will admit that I'm not sure at which stage of the line's evolution, but I personally don't mind if a light does not bother me and I don't plan on putting myself in a situation where it could make a difference, like trying to stop the fast moving blades of a huge propeller


----------



## reppans

Yeah the Minis are generally fast enough to be hard to visually notice... but that line's efficiency, unfortunately, takes quite a hit .


----------



## Cataract

@ reppans: tint shift VS current input (or difference in tint on lower modes) seems to be much more obvious on modern high power LED's from what I read around here, but I admit that I barely can see it myself. 

By "temperature regulated", do you mean the light gets hot or the tint shifts a lot?


----------



## reppans

The bulk of my collection are EDC AA/14500 lights so I'm usually below ~400 lms @ Max - so I guess I'm not really in the "high powered" class . 

Temperature regulation is an weird MDC thing - its moonlight output will vary 4x from 0.15 to 0.6 lms depending upon the temperature of the head (from >80F to <60F, respectively). So while it doubled the lm-hrs efficiency of my CR lights @60F (in a chilly attic), it might have also come in half as efficient if tested during the summer heat.


----------



## Cataract

Interesting... 

400 lumens is still a lot more than you need unless you're in deep, deep doo-doo IMO. 

That temperature related regulation issue is kinda weird and not so weird for someone who understands electronics to a deep level. Temperature related resistivity is definitely a subject for another thread, although it is worth mentioning in here just to get people to understand how many factors can enter the equation.


----------



## SemiMan

reppans said:


> I also wonder about current regulation efficiency thing too..



LEDs are more efficiency current dimmed down to about 5% of maximum. Below that, you are better to drive them at 5% and PWM them. As well, your circuitry is likely to be more efficient this way too.

Semiman


----------



## Cataract

*
{disclaimer for all readers}*:


I realize how the latest posts seem like they might not be directly related to the original intent of this thread/sticky, but, as this thread is due to mature, I welcome them as an introduction to how wide the entire world of flashlight "regulation" really is. 

I also want to mention that there are no reasons (other than subjective preference ) to reject a potential light based simply on any single spec alone; If it's in your hands and allows you to see and do what you need to do without annoyance or hindrance, this light is your best friend in the situation you are in. That is my pure and honest opinion. 

When I started this thread, I simply wanted to help people understand the element of PWM (Pulse Width Modulation) since I saw many member struggling to understand what it is at the time I wrote the original post. I have been made to feel I achieved this purpose with all the positive feedback and I thank you all for letting me know I helped in understanding the phenomenon. All "thank you" notes are definitely warmly welcomed. These let me know I have achieved my goal and definitely encourage me in making an effort in keeping this thread up to a certain standard. Such remarks also inspired me in writing an article at work on basic lithium-ion battery care, which I will likely share here in the near future. It is my turn to thank you for letting me know I was able to help and for the strength you gave me to put the extra effort needed. I did get good words from my boss and I feel I owe it to you all here and to those who gave me feedback in my "basic flashlight troubleshooting guide" thread.

I now hope the extra information contained in the later posts may help the more curious people and followers to understand how much more is really involved in making a well made "regulated" light and that PWM is not necessarily evil. I do my very best to keep things simple or, at least, interpret what is being shared with as much simplicity as I can as people share more directly or indirectly relevant and expansive information on the core of the subject of LED "regulation". This is not easy to do as a thread is fluid and is built on as many points of view as there are participants. To top that off, I also do tend to many other hobbies at the same time (and try to have a life too  ) 


A BIG thank you to all that have shared from post 2 to this post and I feel this is all going on very well.


----------



## Cataract

SemiMan said:


> LEDs are more efficiency current dimmed down to about 5% of maximum. Below that, you are better to drive them at 5% and PWM them. As well, your circuitry is likely to be more efficient this way too.
> 
> Semiman



Wow, nice short and sweet explanation, I did not know this myself... Thanks! 
(BTW, I believe you meant "you are better to drive them at 5% *from maximum *and PWM them.[...]"


----------



## hiuintahs

Cataract said:


> Wow, nice short and sweet explanation, I did not know this myself... Thanks!
> (BTW, I believe you meant "you are better to drive them at 5% *from maximum *and PWM them.[...]"


No..........5% of maximum......down near off. But I probably should let Semiman speak for himself.

From 5% up to 100% is current regulated. But below 5% you set the current at 5% such that a 100% PWM duty cycle you get 5% of the maximum current. Then as the duty cycle ratio drops, the average current does also. For example a 50% duty cycle would then give 2.5% output.


----------



## jon_slider

hiuintahs said:


> ... From 5% up to 100% is current regulated. But below 5% you set the current at 5% such that a 100% PWM duty cycle you get 5% of the maximum current. Then as the duty cycle ratio drops, the average current does also. For example a 50% duty cycle would then give 2.5% output.



Thanks for the info!
That model fits the Prometheus Beta Copper pretty closely... a 25% duty cycle of 5% of 85 lumens, would give 1 Lumen of high CRI from the N219, Im even more tempted to buy one now .. you guys are costing me money, lol


----------



## reppans

Thanks guys, so from what I'm hearing above, if I were looking for the most efficient light (assume 100 lms Max), it would be current regulated between 5 and 100 lumens, and then for any mode below 5 lumens, it would be current regulated to 5 lumens, and then PWM driven below that. 

This does make sense, as I find my current regulated lights have their highest efficiency (in terms of lumen-hours) around the middle 2/3rds of their output range (~250 lms-hrs/Eneloop) and they start falling off hard on low lows (<100 lm-hrs/Eneloop @ sub-lumen) and high highs. 

The Malkoff MDC AA is not using the CR-to-5%-then-PWM thing though - this light is pure PWM (aside from max) light - medium is PWM and Gene has mentioned he does not have the technology to do CR. But it does make sense that a pure PWM light like this could yield ~200 lm-hrs at both medium (~11 lms) and also still on its sub-lumen mode (with the only diff. being duty cycle). 

Think I have reconciled this my mind now.... thanks, and I appreciate the input.


----------



## Cataract

hiuintahs said:


> No..........5% of maximum......down near off. But I probably should let Semiman speak for himself.
> 
> From 5% up to 100% is current regulated. But below 5% you set the current at 5% such that a 100% PWM duty cycle you get 5% of the maximum current. Then as the duty cycle ratio drops, the average current does also. For example a 50% duty cycle would then give 2.5% output.



Ah, got it... makes more sense this way... it is hard to drive anything at a very low current without losing efficiency.


----------



## Cataract

reppans said:


> Thanks guys, so from what I'm hearing above, if I were looking for the most efficient light (assume 100 lms Max), it would be current regulated between 5 and 100 lumens, and then for any mode below 5 lumens, it would be current regulated to 5 lumens, and then PWM driven below that.
> 
> This does make sense, as I find my current regulated lights have their highest efficiency (in terms of lumen-hours) around the middle 2/3rds of their output range (~250 lms-hrs/Eneloop) and they start falling off hard on low lows (<100 lm-hrs/Eneloop @ sub-lumen) and high highs.
> 
> The Malkoff MDC AA is not using the CR-to-5%-then-PWM thing though - this light is pure PWM (aside from max) light - medium is PWM and Gene has mentioned he does not have the technology to do CR. But it does make sense that a pure PWM light like this could yield ~200 lm-hrs at both medium (~11 lms) and also still on its sub-lumen mode (with the only diff. being duty cycle).
> 
> Think I have reconciled this my mind now.... thanks, and I appreciate the input.



Good luck finding a manufacturer crazy enough to come up with a light that combines CR and PWM, although I think I met someone who might be just crazy enough to venture that way while I was digging the tunnels around here. It definitely wouldn't be a 100 lumens max light, though...


----------



## Hondo

Henry is that crazy. My HDS Basic42 has no PWM until you get to the real low modes. Then if I look for it, it is clearly there. It seems he still uses something like this, but maybe more like the Quark "warble" effect, I can't tell. It is hard to say that there is any fluctuation on the new lights by eye, but one of reppans' photos in the HDS thread shows something on the sub-lumen mode like what I have in some Quarks, but much faster and maybe with less % variation in brightness.


----------



## Cataract

A well-made (high frequency) PWM circuit can be extremely hard to detect. I remember some older review from Selfbuilt that could only detect the PWM on the scope... something like 10Khz! God forbids I would remember which brand, though.


----------



## jon_slider

some info I found educational, though older than the current Rev 3 Maratac. If anyone has specific PWM frequency info for any of the lights being discussed in this thread, please share links to reviews and facts. Specific examples of lights with specific PWM specs would be very helpful imo.

http://forum.multitool.org/index.php?topic=15912.40;imode
"PWM is a way to offer lower output levels without having to reduce the current to the LED. 


With the E01's circuit, the current can just be set to the desired drive level. With a Maratac or a Fenix LD01, the drive current is set for the max level, and PWM is employed for med and low levels to reduce the output. Basically, the LED is driven at the same current for the med and low levels, but since the LED isn't powered 100% of the time, output is reduced and runtime is increased.

Other lights, such as the rest of the Fenix line, use a separate current driver circuit for each level offered. This is a more expensive, yet more power efficient way of offering multiple levels in one light. The price of the circuit is not the only consideration when the decision is made to include PWM or current regulation into the design of the light. Other considerations are space constraints (size of the circuit board), and how many levels are going to be offered. If many levels are offered, such as in the NiteCore D10, a PWM circuit will most likely be used."


----------



## masterP

no reply from Surefire or Foursevens, even after several emails asking about some of their products

only reply was from Fenix

the Foursevens Preon Penlight is current controlled, not PWM. that might be my next purchase. I like the style and no strobe, SOS, or beacon modes!!!


http://budgetlightforum.com/node/20822


http://www.candlepowerforums.com/vb...xAAA)-Review-RUNTIMES-BEAMSHOT-VIDEO-and-more!


----------



## jon_slider

masterP said:


> the Foursevens Preon Penlight is current controlled, not PWM. that might be my next purchase.



post a review  The preon seems like a nice smooth package.

I have an aaa light with PWM, that uses the N219 High CRI Led. Im so blown away by the colors, Im shopping for a non PWM with N219. I found the L3 Illumination L08, its next on my list. After that Im hoping to get some CRI readings comparing the PWM N219, to the Current Controlled N219, to see if it is true that PWM gives higher CRI on low modes.

I strongly recommend you include color temperature in your considerations. Another non PWM N219 aaa is the EagleTac D25 AAA


----------



## masterP

thanks for all the info guys.....just bought a Preon Penlight for my father. no PWM




pictures upload


----------



## scs

To folks who are sensitive to PWM and/or experience discomfort from PWM, does the tint influence the severity of your sensitivity and/or discomfort?
Anybody here who still perceives and/or feels the presence and/or effects of PWM @ 2+ kHz?


----------



## Cataract

My few PWM lights are cool white so I can't say for sure, but I don't think I would be much less disturbed if they it had a neutral or warm LED in them. It might feel a tiny bit less aggressive for me IMO.

As for frequency I never gathered the exact frequency info for my lights so I don't really know either. The consensus in the past was that at 10KHz+ it should be absolutely undetectable, although a few have said that it was still unbearable for them. Some still prefer PWM lights as they say they hate the tint shift they perceive from current controlled lights on very low modes, but they mostly choose ones with a high enough frequency (IIRC something like 4kHz and up, depending on personal preference). 

In the end, there is a very personal or subjective component to perception to PWM frequency and tint shift, but there is a majority of people who agree to certain limits. Hopefully some people will chime in and help you get a more definite answer to your question.


----------



## Cataract

masterP said:


> thanks for all the info guys.....just bought a Preon Penlight for my father. no PWM



That's great!


----------



## jon_slider

http://www.flashlightreviews.ca/Preon.htm
"the Preons use pulse-width-modulation (PWM) for their Lo/Med modes."

Some single AAA drivers that I know of that use No PWM are, thrunite Ti3, Olight i3s, Fenix E05 2014, L3 Illumination L08, Prometheus Beta aluminum and nickel

Some single AAA drivers that I know use PWM include, Maratac Rev 3, Prometheus Betta Copper, Preon 1 and 2

Some single AAA drivers that use no PWM but have a sawtooth wave are DriverVN, and Eagle Tac D25aaa


----------



## more_vampires

A CPF'er was telling me that the only way to the non-PWM Maratac rev 2 was to driver swap as previous poster mentioned. At time of posting, only the rev3 drivers are available if you wanted that copper host body.

Hate it when a maker of an awesome host body adds a feature that some of us don't like...

That said, I'm sure plenty of people will go for the rev3. It's all in what you prefer.


----------



## jon_slider

A new way to detect PWM, use the spin cycle
see the 4minute 15second mark… 

Quiz, why are there dots, instead of a constant streak of light?


----------



## Cataract

I've washed many lights by accident, but I have never thought of putting one in on purpose while it was on! Maybe I should EDC my lights in my socks so they don't clank around the dryer like crazy... Good find though. Makes me wonder how fast my washer spins so I could calculate the maximum PWM frequency I could detect this way.


----------



## JenniferMa

very nice article,thank you.


----------



## tbx8192

Very good topic. So CC is always better than PWM.
Is there a list of flashlight that uses PWM?


----------



## Bullzeyebill

PWM is used in conjunction with a CC driver for dimming in many lights. Some PWM/CC lights do not show a strobe effect, they are so fast. The dimming modes are still CC. Maybe this has been brought up in a previous posting in this thread.

Bill


----------



## bkpdle

tre said:


> Nice job explaining PWM. There have been a lot of PWM related threads recently and a lot of people thinking it is all bad. I have no problem with it if the frequency is high enough. My Zebralight SC51w has very slow and noticable PWM on the lowest mode. Oddly my other Zebralights have no such "slow PWM" on their lowest modes. Anyway, my point is that now people should understand PWM, and realize that it is not a problem (if it is fast enough).



I was wondering about the Zebralights. Are all their lights PWM? It seems every AA light I look into operates on PWM. I assume HDS Systems lights are not PWM (please correct me if I'm wrong), and SureFire is not, but all these run on 123A. All the AA lights I find myself taking a liking to use PWM.


----------



## KeepingItLight

bkpdle said:


> I was wondering about the Zebralights. Are all their lights PWM? It seems every AA light I look into operates on PWM.



One way to answer this question is to check whether there has been a review. Flashlight reviewer Selfbuilt _always _comments on PWM, either to say he found it or he did not. Zebralight is a brand Selfbuilt frequently reviews. In his review of the *Zebralight SC5*, a 1xAA flashlight, here is what he said:



selfbuilt said:


> *PWM/Strobe*
> 
> As with my other Zebralight lights, I don't see any signs of pulse width modulation (PWM) on any the lower output modes. The light appears to be fully current controlled at all levels.



I believe it has been several years now since a new Zebralight model used PWM.


----------



## scs

Bullzeyebill said:


> PWM is used in conjunction with a CC driver for dimming in many lights. Some PWM/CC lights do not show a strobe effect, they are so fast. The dimming modes are still CC. Maybe this has been brought up in a previous posting in this thread.
> 
> Bill



Thanks for mentioning this. I have not seen it brought up. I was only recently informed that CC and PWM are not exclusive, that, as you mentioned, some CC drivers use PWM for the lower output levels. It seems that if there's no PWM then the driver is CC, but it's not always the case the other way around.


----------



## Hondo

Here is what my cob-web ridden brain recalls:

Zebralight: The older models do use visible PWM on SOME modes, like L1 might be CC, and L2 PWM. Later models seem either all CC or so high frequency PWM as not to be noticeable.

HDS: The original HDS lights (B42, U60) did have visible PWM on lower modes. Now you can't see it, but I think Henry uses a special voodoo mix of high frequency PWM and current control on lower modes to help control the tint shifting you can get with pure CC at low currents.


----------



## Cataract

Zebralight made a move to 100% current regulation a couple of yeas ago. If they had a model that used PWM regulation, they would certainly mention it AND the frequency used, as they did for their later PWM driven models.


----------



## jon_slider

Hondo said:


> to help control the tint shifting you can get with pure CC at low currents



I agree tint shift avoidance is a feature of PWM. That advantage may dim below 3 lumens, and may be moot on a low CRI LED:
https://en.wikipedia.org/wiki/Mesopic_vision
"Mesopic light levels range from luminances of approximately 0.001 to 3 lumens"
"Humans see differently at different light levels. This is because under high light levels typical during the day (photopic vision), the eye uses cones to process light. Under very low light levels, corresponding to moonless nights without electric lighting (scotopic vision), the eye uses rods to process light. At many night-time levels, a combination of both cones and rods supports vision. Photopic vision has excellent color discrimination ability, whereas *colors are indiscriminable under scotopic vision*. Mesopic vision falls between these two extremes. In most night-time environments, there is enough ambient light at night to prevent true scotopic vision."


here is a tangent link about low light levels and color vision:
Foreground light, pupil constriction, color temp and color spectrum.
"A fairly recent development, i.e. < 10 years ago, has shown that pupil/iris response/opening is actually tied to melanopsin sensitive ganglion nerve cells which are a newly discovered third set of sensors within the eye. They are also primarily responsible for circadian rhythm."


----------



## GeraldLCPD

Thanks
Good Explanation.

Looks like my PWM Test was wrong after all. to be honest, my reviews were wrong also.
I'll fix my way to test PWM now


----------



## Cataract

GeraldLCPD said:


> Thanks
> Good Explanation.
> 
> Looks like my PWM Test was wrong after all. to be honest, my reviews were wrong also.
> I'll fix my way to test PWM now



Why do you say your test was wrong? Did you find that some of your lights actually have PWM that you had not detected before?


----------



## BugoutBoys

Cataract said:


> PWM is very often misunderstood or simply an unknown thing for most newbies and some older CPFers and I would like to offer the simplest explanation of what it is, how to detect it and why it is not such a good thing after all. I will do my best to avoid advanced explanations of what is the difference between voltage and current, as there are plenty of resources to learn about that, and it is definitely not a pre-requisite to understand what I’m about to reveal.
> 
> 
> FIRST OFF : The basics of lighting a L.E.D.
> 
> -L.E.D stands for Light Emitting Diode. A diode is a basic component of electronics that will allow current to flow in only one direction: form positive pole (or lead) to the negative pole of your battery.
> 
> -LED’s need a specific voltage to work properly. Originally, LED’s could only give off a fixed amount of light because the circuits controlling them would only give a fixed amount of volts, which translated in a fixed amount of current.
> 
> -There are two ways to control –that is lessen- a LED’s light output: limit the current going through the LED with sophisticated circuitry, or use PWM. Current limitation is a lot more complex and more expensive mostly because the circuit has to be designed according to the specific LED’s characteristics, in accord with the type of battery being used.
> 
> 
> PWM for Dummies
> 
> -PWM stands for Pulse Width Modulation.
> 
> -Rather than limiting or controlling the voltage or current going through your LED, the voltage is fixed. When the full DC (Direct Current) voltage is sent through the LED, it will emit the maximum of light it can (basically the same as connecting directly to a fully charged battery)
> 
> -In order to allow for lower modes, this current will be transformed in a high frequency current that can allow for less total “potential” (read current) to be sent through the LED. Let’s use graphics:
> 
> Direct Current (basically, the constant voltage a normal battery will give off. I ignore the normal discharge curve for this example and let’s imagine our battery has unlimited charge):
> 
> 
> 
> 
> 
> 
> 
> With such an input, it is obvious that our LED will emit a fixed amount of light. Now, if we introduce PWM:
> 
> 
> 
> 
> 
> 
> As you can see, we have now changed our constant voltage input for a square wave. In this graphic, our voltage is on half the time and off half the time. The technical term here would be that we have a 50% duty cycle (50% of the time on.) With such an input on our LED, the amount of light given off appears diminished by 50%. The reason I say it appears, is because it gives off its maximum amount of light, but only 50% of the time, so our eyes perceive only half the amount of light (more on this in the next section).
> 
> I we wanted an even lower perceived light output, let’s say 25% of the maximum, we would use a PWM input that would look like this:
> 
> 
> 
> 
> 
> (Disclaimer: I’m stuck using Paint to draw these graphics, so it might not be 100% up to scale)
> 
> In this graphic, you can see that the voltage is on only 25% of the time, in technical terms we have a 25% duty cycle, but the voltage is still switched _on_ at the same intervals as in the previous graphic. This basically means that we have a fixed frequency (number of times we switch the power on and off per second).
> 
> So, Pulse Width Modulation simply means that we control our light with pulses and we vary (modulate) the width of these pulses to control the amount of perceived light to less than the maximum amount the LED can give off.
> 
> How Come I _Perceive_ Less Light And No Blinking Or Strobing??
> 
> Your eyes are a little like tiny cameras that take about 24 pictures per second. Your brain takes those images and assembles them into what we perceive as the continuous movie of our lives. If the PWM frequency was less than 24 times per second (or only slightly more), we would perceive it as a strobe, but if the light from a PWM controlled LED is switched fast enough – way more than 24 times per second – our eyes will perceive it as continuous... but there’s an IF here:
> Let’s see through graphics what would be the main difference between a lower frequency and higher frequency PWM
> 
> LOWER FREQUENCY PWM:
> 
> 
> 
> 
> 
> 
> 
> HIGHER FREQUENCY PWM:
> 
> 
> 
> 
> 
> 
> 
> In both these graphics, the power is on half the time (50% duty cycle), but in the second graphic, the power is switched more often.
> 
> HOW DO I PERCEIVE PWM CONTROLLED LIGHTS??? HOW DOES IT AFFECT ME???
> 
> The lower frequency PWM will be more perceivable to the eyes as a fast strobe effect – remember what it looks like to dance in a club when the only lighting around are strobes? Well, imagine that strobe is even faster, to the point that motion is almost continuous...
> 
> With any frequency of PWM, if you sit still and stare at a fixed spot on the white wall across from you while pointing your favourite PWM controlled flashlight at it, you will never know the difference. With a PWM frequency that is too low for your perception (and this frequency is very likely to vary from one person to the next) you will definitely perceive a form of strobe effect; if you wave your hand fast enough in front of the light, it might look something like this:
> 
> 
> 
> 
> 
> 
> Count how many thumbs I appear to have. Try waving your hand in front of your camera with normal lighting and I promise you will not see repeated edges like on this photograph.
> 
> This effect can be seen with anything that moves in relation to your eyes, but that movement has to be fast enough in relation to the PWM frequency and your own perception for you to be able to perceive it. Some people see it more, some people see it less.
> 
> If you find out your favourite reading light has bad PWM effect when waving your hand in front of it, but never use it for anything else, it might still be very useful to you. If, on the other hand, whenever you read by flashlight you get a headache, it might be worth trying another light just to see if there is any relation. I know PWM can affect me in some ways and I’ll get to that later (of course, it doesn’t mean everyone is affected, but some applications are definitely more critical than others)
> 
> 
> How Can I Detect PWM On Higher Frequency Lights?
> 
> AAhhhh.... I only ask this question because I found a very nice answer to this one that doesn’t involve taking your light apart or expensive electronic equipment. Waving your hand in front of, let’s say a Quark Mini, will not show any signs of PWM... but the Mini’s ARE PWM controlled! The frequency used is simply high enough that you will not (or not likely) perceive it when using the light. So how was I able to tell that without even opening it up?
> 
> This kinda brings me to a very old stupid joke that I will botch on purpose here: Normal people cool down by waving their hand in front of their face... Niewfies wave their face in front of their hands. Well... turns out this is pretty much the best way of detecting PWM on a flashlight (WAIT! There’s a twist to this... don’t risk blinding yourself or getting a neck injury before reading the rest!) Rather than waving your hand in front of your light, wave your light in front of your face. NOW, PWM will be easiest to detect on you light’s lowest mode (remember about duty cycle? Lower duty cycle = more space between pulses.) Second, you don’t need to send the lights directly into your eyes... just hold it so you can see the light on the side of the reflector as such:
> 
> 
> 
> 
> 
> 
> Turn the lights down if necessary, so you can see the light clearly enough and now wave it sideways like this:
> 
> 
> 
> 
> 
> 
> This is a picture of a constant current light. Any of your lights on maximum current should look exactly like that.
> 
> Here’s a picture of bad PWM:
> 
> 
> 
> 
> 
> (Note: please respect your articulation’s limits... if you can’t see it, it might not be there)
> 
> Notice how we can see individual and separate spots of the same light’s business end? And I wasn’t moving very fast at all... In this case, just waving your hand or fingers in front of it will reveal the PWM even with a certain amount of ambient light.
> 
> Here is what “good” PWM looks like:
> 
> 
> 
> 
> 
> 
> Let’s zoom-in on that picture:
> 
> 
> 
> 
> 
> 
> This type of high frequency PWM is very hard to detect and is very unlikely to affect you under any circumstances; It can only be detected efficiently using this precise method and a camera also helps if you can catch your hand in just the right time.
> 
> 
> 
> What Are The Other Uses For PWM?
> 
> PWM is mainly used to control electric motors (like hybrid cars), but mostly step-motors like the ones in your hard-drive.
> 
> Tons of newer cars have LED’s for daylights and rear position lights. As we all know the very same rear position lights are often also used as brake lights, so these lights need to be dimmed to differentiate from when a driver applies the brakes. Some manufacturers –perhaps most?- use PWM to achieve this, but some of them use a very (or failry) low frequency of PWM that actually affects some people, like me. I believe there is a more and more urgent need to sensitise manufacturers as the effects can be very uncomfortable for the eyes of some people. Just as an example, when I drive at night behind some models of Cadillacs or Volvo’s, I either slow down drastically to let them out of my sight or pass them as fast as reasonable (sometimes over the local speed tolerance) because it tires my eyes badly.
> 
> 
> WHY PWM?
> 
> Using PWM to control a light’s output is simply cheaper, because so many existing Integrated Circuits sold off-the-shelves can do it and all that’s left for the manufacturer is to add a small circuit that controls the Duty Cycle or frequency. There is very little measuring, calculating, tweaking and experimenting needed from the manufacturer’s engineering department, so money is saved on manufacturing, parts AND research.
> 
> 
> Conclusion
> 
> Well, there you go. Feel free to ask questions and I’ll answer to the best of my ability. Also, feel free to share your take on PWM, whether you’re a beginner or an expert on the subject. This could also be a good place to list light that are controlled by PWM and how much it shows and affects usage.



Probably the best explanation I have seen!


----------



## jon_slider

Some Examples of PWM

I just received a Copper Tool Clickie and a Maratac Rev 3 latest stock. It appears the latest Maratac does not use PWM like the Rev 3 earlier run did.






My iPhone sees the PWM much more obviously than my naked eye. Both lights are on Medium in this next photo:





Neither light has PWM on high:





When I wave the lights, the PWM is more obvious to my naked eye, than to the camera.





You may also notice that on Medium the Maratac tint is not as white as the Tool. I think thats the result of the difference between PWM lighting the LED in pulses at full power, hence full brightness, and the apparently Current Controlled latest Maratac, experiencing some tint shift towards a slightly warmer tint. Both LEDs are XP-G2.

PS, it can be very difficult (for me) to determine if a light uses PWM or not just from reading specification pages, for example:
"Digitally regulated output maintains constant brightness"
That is the spec for the Lumintop, which as Ive shown, Does Use PWM. The words digitally regulated is unclear, as it could mean Pulse width modulation (thats digital), but it could also mean current regulation (also digital but used to refer to non PWM circuits). The hint is the term constant brightness, which is in fact what PWM accomplishes by pulsing at full power, the brightness of the LED is constant, and does not dim as it does with current regulation. Note the word regulation has also been used in both PWM and Constant Current specs, adding to my confusion. For example Fenix, which makes non PWM lights, specifies "regulated current".

So I leave you with a couple of terms to consider, regarding how the circuits produce the lower modes.. 
*PWM = Constant Color*… (led flashes on and off at full power)
*Non PWM = Constant Current* (led stays on constantly, at less than full power)


----------



## Cataract

BugoutBoys said:


> Probably the best explanation I have seen!



Thank you sir!


----------



## Cataract

Nice Pics and observations jon_slider, exccept one small detail



jon_slider said:


> [...]*The hint is the term constant brightness, which is in fact what PWM accomplishes by pulsing at full power* *(1)*, the brightness of the LED is constant, and does not dim as it does with current regulation. *Note the word regulation has also been used in both PWM and Constant Current specs, adding to my confusion(2)*. For example Fenix, which makes non PWM lights, specifies "regulated current".
> 
> So I leave you with a couple of terms to consider, regarding how the circuits produce the lower modes..
> *PWM = Constant Color*… (led flashes on and off at full power)
> *Non PWM = Constant Current* (led stays on constantly, at less than full power)



(1) I believe what manufacturers mean by "constant brightness" is that the output of each mode will be the exact same as intended for as long as the battery has enough power to sustain it rather than letting output sag with a battery that is getting weaker. Both PWM and constant current circuits can achieve this.

(2) Somewhat of a legal matter term IMO: "Regulated" or "Regulation" only mean that the output (brightness) is being regulated, which could or could not mean the same as "constant brightness" and does not necessarily refer to the means by which this is achieved (PWM, CC or other). The word "Regulated" does not exclude cases where the output is not all that constant and dims as the battery is getting weaker, like some cheaper imported lights. Even in this case, it is not a lie, the output IS regulated to less than maximum output, just not with a constant brightness. 

The Predator has an option to use this type of regulation where the output sags over time, which can extend the effective runtime by quite a bit. It is also sometimes preferable to see your light slowly dim rather than suddenly die as you step over the edge of something... That only happens on the lowest mode of course, but I've had it happen to me once and it wasn't exactly fun.


----------



## Timothybil

Ran across something interesting tonight. I was trying to scan a Walmart qcode with my AT&T android scanner app, and was using my EA11 in low mode to add a little light. I knew the EA11 used PWM, but it was really interesting to see interference bars running across the scan display as I was trying to scan the code. Apparently the PWM off period was wide enough, and the rear camera on my Nexus 7 sensitive enough to register the light differences of the PWN on and off phases.


----------



## jon_slider

Cataract said:


> Nice Pics and observations jon_slider, exccept one small detail
> 
> (1)..."constant brightness"… Both PWM and constant current circuits can achieve this.
> 
> (2) ..."Regulation" only mean that the output (brightness) is being regulated, which could or could not mean the same as "constant brightness" and does not necessarily refer to the means by which this is achieved (PWM, CC or other)….



Thanks for illuminating my confusion

Current Controlled, sometimes means No PWM
Regulated, sometimes means No PWM

but regardless what words manufacturers use to add to my confusion, I can spot PWM by waving the light

I can also spot the new No PWM circuit in the latest Copper and Titanium Maratac aaa lights, and the latest Lumintop aaa Tool, both copper and Aluminum, by the ring in the new reflector...

On left, previous model Lumintop Tool, and Maratac used PWM. Note the new ringed LED reflector on right


----------



## Cataract

Timothybil said:


> Ran across something interesting tonight. I was trying to scan a Walmart qcode with my AT&T android scanner app, and was using my EA11 in low mode to add a little light. I knew the EA11 used PWM, but it was really interesting to see interference bars running across the scan display as I was trying to scan the code. Apparently the PWM off period was wide enough, and the rear camera on my Nexus 7 sensitive enough to register the light differences of the PWN on and off phases.




Barcode + PWM... good one! You should have taken a picture with the barcode both horizontal and vertical just for fun


----------



## Cataract

jon_slider said:


> Thanks for illuminating my confusion
> 
> Current Controlled, sometimes means No PWM
> Regulated, sometimes means No PWM
> 
> but regardless what words manufacturers use to add to my confusion, I can spot PWM by waving the light
> 
> I can also spot the new No PWM circuit in the latest Copper and Titanium Maratac aaa lights, and the latest Lumintop aaa Tool, both copper and Aluminum, by the ring in the new reflector...
> 
> On left, previous model Lumintop Tool, and Maratac used PWM. Note the new ringed LED reflector on right




Glad I can help 

Current Controlled usually means no PWM, but there are exceptions.

Nice Cu lights BTW... the Maratac has a slightly beefier look in this pic along with the ringed reflector.


----------



## Timothybil

Cataract said:


> Barcode + PWM... good one! You should have taken a picture with the barcode both horizontal and vertical just for fun


I would, except I was scanning a QCode, which is that little square with the tiny blocks all over it in some weird pattern. I'll try it on a bar code one of these days.

BTW, the light/dark bars pattern was across the entire screen, which included the desktop behind the receipt being scanned.


----------



## Cataract

Timothybil said:


> I would, except I was scanning a QCode, which is that little square with the tiny blocks all over it in some weird pattern. I'll try it on a bar code one of these days.
> 
> BTW, the light/dark bars pattern was across the entire screen, which included the desktop behind the receipt being scanned.



A QR code is a 2D barcode (don't mind the fussiness, I used to work in the barcode business). Doesn't matter the type of barcode or what you are aiming at; if the brightest source of light in the focus area of the camera is PWM driven, I suspect it will manifest all over the picture. The one thing is that CCD pixels are scanned horizontally, that is why we always see the interference as horizontal bars on digital pictures. It is all a question of how fast the pixels are converted to data and how fast your light "blinks".


----------



## BYD-bateria

Nice job
I suggest you reverse engineer your solution. There are dozens of plug-them-in-an-outlet emergency lights on the market. Find one that matches closely your ideal, buy it, and hack it. You will likely be seeing the UL aspects battery needed in the device you dissect.


----------



## Hiker

I have noticed that when I put my single AAA Fenix against a window I hear a high pitched whining sound. I assume that is the PWM so this is probably another way to test it.


----------



## jon_slider

Hiker said:


> … high pitched whining sound. I assume that is the PWM…



thanks for that insight, it is new info to me. I usually notice PWM when taking photos, or I can detect it by waving. 

Feel free to add the Fenix to this thread if you like: (please include specific model info)
List Lights that use PWM

I read recently that the Malkoff MDC is a PWM light known to have a circuit noise like you describe


Grizzman said:


> Yes, the multi-level MDCs do use PWM. Some lights exhibit louder whine than others, with mine only being audible when the light is pressed against my ear.


----------



## Heavy

Fantastic explanation! Thanks so much.

If I am not mistaken this is the same type of system that is used in florescent bulbs yes?

They run, or are supposed to run, at a rate that the eye can't see. 

This is why I ask. I have a huge problem with fluorescent lights. Just a few minutes under them and my eyes are super tired. I notice that if the ballasts that control that rate of speed gets old I swear I can see them pulsing. 


So my question is this. Is this the same way LED bulbs for your house are controlled? Because if they are then I worry that they will bother me also.


As you can see from my post I know just enough about lighting to know that I don't know much.


----------



## FRITZHID

Heavy said:


> Fantastic explanation! Thanks so much.
> 
> If I am not mistaken this is the same type of system that is used in florescent bulbs yes?
> 
> They run, or are supposed to run, at a rate that the eye can't see.
> 
> This is why I ask. I have a huge problem with fluorescent lights. Just a few minutes under them and my eyes are super tired. I notice that if the ballasts that control that rate of speed gets old I swear I can see them pulsing.
> 
> 
> So my question is this. Is this the same way LED bulbs for your house are controlled? Because if they are then I worry that they will bother me also.
> 
> 
> As you can see from my post I know just enough about lighting to know that I don't know much.



Older florescent lighting used the A.C. line freq of 60hz so the bulbs flashed on and off at a rate of 120/sec. Newer versions use electronic ballasts that on higher end use very high freq so flicker "sickness" is minimised. LED lighting that uses PWM control can cause this as well however many use either high freq PWM or current control to fix that issue, espc in home LED lighting.
There are many reviews on cpf that will show you which are the worst/best.


----------



## kj75

A example I want to share with you.
Found during my first dinner at my holiday resort, I noticed this terrible bulb. 
Look at the picture taken with my cell phone.


----------



## jon_slider

kj75 said:


> terrible bulb.


great photo!
before taking the photo, did you think there was PWM happening? 
what did you notice about the lighting that made you investigate?


----------



## kj75

jon_slider said:


> great photo!
> before taking the photo, did you think there was PWM happening?
> what did you notice about the lighting that made you investigate?


I was cleaning the table and noticed this while whiping with my hand.
Took the picture to show and explain my sons.


----------



## jon_slider

kj75 said:


> noticed this while whiping with my hand.



I had a similar experience with my LED house lighting. I was wiping my hand back and forth on a piece of leather on the table, to polish a knife. It looked like my hand kept stopping. I went online and researched home led lighting and PWM. Turns out many home systems use PWM for dimming, including unfortunately, my Phillips Hue System.

But thanks to your photo, I just did a series of tests, to see if Phillips Hue only Pulses during dimmed output. Unfortunately no, it pulses even on high. So, Im the guy that sold all his PWM based flashlights, paid to swap drivers to no PWM multiple times in others, and here I am sitting in my kitchen under a PWM light source.. hmmmm.. I guess people should feel welcome to laugh at me , including myself..

warm white shows PWM in the photo, both on high and also on a dimmed mode not shown









cool white on high the PWM is not visible in the photo









cool white dimmed, reveals PWM in the photo









the red led does not show any PWM in photos


















not all conditions will capture PWM in a photo, I found red and blue do not reveal PWM, but yellow, white, and even green do show the interference bands in the photos. At first I though that it would not happen on high, only on dimmed levels, but no, PWM is present even at full brightness, and can be photographed quite easily on the Warm White setting. All photos from my iPhone 5, no special white balance nor other adjustments.


----------



## kj75

Thank you @jon for your effort!
Now we have to check all our house led lighting too


----------



## SemiMan

There are a several things to consider about whether a light is going to bother you, one is modulation depth (how deep the flicker is), the other is frequency of the flicker, and the shape of the flicker can come into play as well.

- The fluorescent lights that bothered you were likely old magnetic ballasts, who flickered at 100 or 120Hz. They did not turn on/of, but they would have peak-peak flicker up to 50% of the average. I.e. they went from 75% - 125% light output
- Electronic fluorescents may have flicker at 100/120Hz, but it may only be 5-10%, and then riding on top of that may be flicker at 20+KHz which is invisible
- CFLs are usually pretty similar
- LEDs for the home are all over the map
- The one in the hotel may have been a so-called AC drive LED which really does turn on/off at 100/120Hz. They are headache machines. Other LED lights for the home typically have anywhere from near 0 to 40-50% flicker, with the bulk it seems in the 20-30% range though as LEDs get more efficient, companies are willing to sacrifice a bit of efficiency for light quality.


----------



## SemiMan

Accidental double post


----------



## jon_slider

SemiMan said:


> LEDs for the home are all over the map… headache machines



Are there ANY home LED lighting systems you know of that dont use Pulses? I removed my Phillips Hue due to the PWM. It did not give me headaches, but the light seemed to make for a "fuzzy" ambiance. (no idea how to quantify that impression)


----------



## FRITZHID

jon_slider said:


> Are there ANY home LED lighting systems you know of that dont use Pulses? I removed my Phillips Hue due to the PWM. It did not give me headaches, but the light seemed to make for a "fuzzy" ambiance. (no idea how to quantify that impression)



GE bright stick. I have a dozen around the house. No noticeable PWM at all.


----------



## Modder

nice post !


----------



## jon_slider

SemiMan said:


> There are a several things to consider about whether a light is going to bother you, one is modulation depth (how deep the flicker is), the other is frequency of the flicker, and the shape of the flicker can come into play as well.



Thanks for the rundown. 
You mention fluorescents, CFLs and LEDs all have flicker. 
*What about incandescent, do they flicker too?*



FRITZHID said:


> GE bright stick. I have a dozen around the house. No noticeable PWM at all.


thanks, I looked it up, 
they are rated for 80CRI.. 
no "noticeable" PWM? Have you tried taking a cell phone photo?

For home lighting, Warm White incandescent with 100CRI and no? PWM are sounding better and better to me.


----------



## SemiMan

Home LED lighting does not have PWM almost as a rule. The flicker is from the 50/60Hz line frequency and circuit\cost tradeoffs.

Incandescent does flicker, just not a lot.


----------



## timsdl72

I apologize ahead of time. I didn't read all 270+ pages before replying so if it's been mentioned before, I'm sorry!

I work as an electrical specialist with the engineering department at a large university. One thing we had noticed is an inconsistency between products that were supposed to be the same item but the flicker was different. What we found was that manufactures were changing suppliers of the LED drivers. I'm sure cost was their reasoning but the result was that the PWM frequency (in the case of motor control VFD's, we call it switching frequency) was different.

Interesting stuff. Thanks for all of the info!


----------



## jon_slider

SemiMan said:


> Home LED lighting does not have PWM almost as a rule.



thanks for your comments


----------



## Bullzeyebill

PM to jon slider.

Bill


----------



## jon_slider

Compare and contrast LED, Incandescent and Daylight tints, as seen by iPhone 5:

Pic 1. Phillips Hue Tri LED home lighting system (91 CRI Pulse Width Modulated) 3000K
Pic 2. 53 Watt Incandescent (100 CRI House Electric) 3000K
Pic 3. Daylight inside, 12 noon, partly cloudy (100CRI sunlight) ~6000K


















And the LED assortment I use at different times of day, photo taken also at 12 noon with overcast sun
XPG2 6000K, N219b 4000K, XPG 3000K (all drivers use NO PWM)
Note the Nichia produces the most realistic Tint match in the color of the Buckskin


----------



## vinhnguyen54

Great PWM write up!


----------



## jon_slider

An example of PWM from an older Maratac, as seen by a video camera (latest models have NoPWM)
https://youtu.be/2jL7TiIQ4yM?t=4m39s


----------



## RI Chevy

Cool video of PWM


----------



## jon_slider

5 seconds of PWM from a McGizmo Haiku:


----------



## ChemicalKraken

Nicely explained. I'm learning a lot just by looking around this forum


----------



## /steve/

Hi there!
I think I found a better way of detecting PWM and even beeing able to estimate the dutycycle!
Today everybody has a smartphone. So just open your camera app and turn on your light and point it as close as possible into your camera. (I don't know how bright the light can be to not kill the sensor, mine camera did 1W just fine). Then you see something like a black pic with white ,regularly appearing stripes(you can see a few of them at once at your screen), depending on your frequency slowly moving to one side. You can estimate the dutycycle from the width of the stripes. I saw that the stripes got more shallow on my minimaglite LED when I switched it into 25% mode.Post some pictures of it if it is working with your Phone's Camera.
have fun
PS: I could see these stripes up to somewhere about 800 HZ.


----------



## jon_slider

> I could see these stripes up to somewhere about 800 HZ.

I hope you post a photo

I also use my phone





this is how I use a piece of printer paper to compare beams. I no longer own any PWM lights, because the interfere with my photos


----------



## jon_slider

Im bringing these forward to help someone who asked in another thread, "How Can I detect PWM?"



reppans said:


> [Eagletac]D25A on 3lms on the left. On the right is a 47s Mini - these are the two fastest PWM lights I've seen - this sweep is as fast as I can move my arm. [middle light is a known NoPWM control]
> 
> 
> 
> 
> 
> 
> ...
> the definitive way to tell is a fast sweep across a DSLR on time exposure, side-by-side with a known fast PWM light, and a true CC light (as above). My own eye-ball detection method is catch the spill in a reflection/mirror and move my eyeballs left to right quickly - I can quite easily see the PWM on the 47s Mini, but it is very hard to detect it on the D25A.





jon_slider said:


> A new way to detect PWM, use the spin cycle
> see the 4minute 15second mark…
> 
> Quiz, why are there dots, instead of a constant streak of light?




-----
Originally Posted by Cataract
wave your light in front of your face. NOW, PWM will be easiest to detect on you light’s lowest mode ...
you don’t need to send the lights directly into your eyes... just hold it so you can see the light on the side of the reflector as such:




Turn the lights down if necessary, so you can see the light clearly enough and now wave it sideways like this:
This is a picture of a constant current light. Any of your lights on maximum current should look exactly like that. [no dots, just blurry streak]





Here’s a picture of [slow] PWM:





Here is what “[fast]” PWM looks like:





----



jon_slider said:


> My iPhone sees the PWM much more obviously than my naked eye. Both lights are on Medium in this next photo:
> 
> 
> 
> 
> 
> Neither light has PWM on high:
> 
> 
> 
> 
> 
> When I wave the lights, the PWM is more obvious to my naked eye, than to the camera.



Other ways to see the effect of PWM
Shine the light at a stream of water from a faucet, or shower. The PWM light will freeze the drops in midair, kind of entertaining. Similar in Snow.

Shine the light at the fanbelt of a car, the PWM light will seem to "stop" the belt, similar to a timing light. This also works on spinning things, like fan blades.

I find my iPhone is quite good at finding PWM if I fill the screen with the light or shoot close range. Waving also works well, its just harder to photograph.

Video also shows PWM in some exposures or angles
McGizmo Haiku:


An older Maratac:
https://youtu.be/2jL7TiIQ4yM?t=4m39s


----------



## neutralwhite

Is 4500hz PWM an issue?.
this is in relation to a pflexpro Nichia drop in I'm considering buying ?.
avoid?.
thanks!.


----------



## vettex2

I have never heard of such a thing, good info


----------



## Hondo

neutralwhite said:


> *Is 4500hz PWM an issue?*.
> this is in relation to a pflexpro Nichia drop in I'm considering buying ?.
> avoid?.
> thanks!.



For me, and 99.XX% of people, no.

Can you still tell it from a non-PWM light if you go looking for it? Yes.

Would I buy it? Yes. Once you get over ~1000 Hz, I don't let that influence my decision at all. And I can tolerate using some of my older lights with 100 - 200 Hz PWM, although I see it a lot in use.


----------



## Lexel

neutralwhite said:


> Is 4500hz PWM an issue?.
> this is in relation to a pflexpro Nichia drop in I'm considering buying ?.
> avoid?.
> thanks!.


 
I have noticed flicker on my budget flashlighs.
I did a photo in my shower with 1/400s and could spot 11 bright and one fade point, so it is probably 4500Hz PWM.

Now I am questioning how I can see flicker at my stillstanding flshlights, on old TV´s or PC Moniotors flicker stopped at 75Hz, 60Hz was a no go for me.


----------



## jon_slider

fwiw, It has come to my attention that some lights that technically do not use PWM, because the Pulses do not drop all the way to Zero, are also NOT Constant Current. My goal in posting this is to eliminate the impression that just because a light does not use PWM, it does not mean it necessarily does not use Pulses that can interfere with Photos.

Examples of lights that do not use PWM by the technical definition, but also are not Constant Current lights, include HDS, Zebralight, Eagletac, and Nitecore lights, that use Pulses that dont drop all the way to zero. More details in these threads:
List Lights that use PWM and or Pulses that are NOT True Constant Current Lights
List Lights that use NO PWM and ARE True Constant Current lights.


----------



## Hondo

Some of my high voltage Quarks exhibit this behavior too. But not all have it. David called it "circuit warble" .


----------



## ridwan_neutron

when im using pwm in flashlight with frequency around 1khz, there is buzzing noise. so i decided to use high frequency pwm around 20 khz and the noise is gone.


----------



## etc

Malkoff M361 uses a flicker rate of 310 Hz. I tries really hard to detect it. No luck with water yet, faucet.
Will try the belt in the car next.

I think there is a threshold where you cannot see PWM. 100 Hz I might see, 300, not. The statement I can see PWM is meaningless because it does not qualify the frequency.


----------



## RI Chevy

Just for the record, as I have previously stated several times. I have 3 M361N's, all of them display PWM on low, and I have the audible whine on low and medium. My eyes and ears can detect it.
With that said, I really like the drop in. Tint is very nice.


----------



## jon_slider

etc said:


> Malkoff M361 uses a flicker rate of 310 Hz. I tries really hard to detect it. No luck with water yet, faucet.
> Will try the belt in the car next.
> 
> I think there is a threshold where you cannot see PWM. 100 Hz I might see, 300, not. The statement I can see PWM is meaningless because it does not qualify the frequency.



PWM is very difficult for most people to detect. There are also lights that produce "noise" that is technically not PWM, but still causes sensitive people to get migraines, such as Zebralight.

when waving a light does not show PWM, even when we know from Malkoff that it is there, another technique that sometimes works is:
taking an extreme closeup of the LED, 
see this post #76 that discusses this photo of a Zebralight:





"noise" is very difficult to photograph, the camera has to be really close, and at just the right distance. 
Video closeups can also show "noise", but again it only works at just the right distance.

imo, it is pointless to argue whether PWM matters or not, if someone does not notice it.
for me, if the light has PWM, or pulses that produce "noise", then it is not Constant Current.
I leave it up to each individual to decide if PWM or "noise" is acceptable.

many, if not most, LED lights use PWM or pulses that produce "noise". Some people get very hostile about being told about it, and make all kinds of excuses why it does not matter to them, and should not matter to me. Im not going to argue about whether PWM matters to me, or someone else, because the conversation becomes hateful and unproductive. Many people Love their Zebras, HDS, Malkoff, etc, and they dont care about "noise" or PWM. So I just report what I find, without expecting to change hearts and minds.


----------



## Hondo

etc said:


> Malkoff M361 uses a flicker rate of 310 Hz. I tries really hard to detect it. No luck with water yet, faucet.
> Will try the belt in the car next.
> 
> I think there is a threshold where you cannot see PWM. 100 Hz I might see, 300, not. The statement I can see PWM is meaningless because it does not qualify the frequency.



If it does not bother you, just enjoy.

I have no problem finding 2,000 Hz PWM when I go looking for it, and I can show it to others as well. I only use the method of holding the light on about a 45 degree angle so I can see into the reflector from the side, and whipping it up and down looking for the "dotted line" of light (as in many photos above, including mine).

Personally, I can use a 100 Hz light. When I move about, I am aware of the strobe-like effect, but it does not give me a headache or anything. But both my wife and I find the 100 Hz PWM LED car tail lamps irritating while driving at night.


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## altendky

Ok, so I read the original post and skipped straight here. Hopefully the misunderstanding has been addressed but in case not...

PWM control does not require that your eyeball or brain be the filter. You can filter the PWM'ed voltage with electronics and have a fairly steady current. This still offers efficiency improvements over analog control circuits and is a much simpler circuit once you have a microcontroller involved. So, PWM in the right circuit is actually a current control mechanism.

Now to guessing. I would expect that even good 'non-PWM' flashlights are still PWM controlled, just using electronics as a filter rather than your eyeballs.


----------



## User 0815

The question is: Where do you put the limit oj what you call PWM free? The more sophisticated your hardware becomes the more lights will "flicker".
Use a clear LED (got mine out of an broken TV remote) hook it up to your scope of liking (software scope works fine as well)
Very basic scope will do:





The low ripple one can see is due to the scope itself. Some lights do really have nasty strobing when pretending to be in low mode ;-)

Regards Peer
___________________________
Please delete below this line. ^^
P.S.: Is one of the mods so kind to fix the picture link of my other post, not shure why the pic does not show up any more, the share is valid? Due to my newbe state you will touch this post anyway - so please fix the other one. Thanks in advance.
For your convinience: https://www.candlepowerforums.com/v...t-use-NO-PWM&p=5198473&viewfull=1#post5198473


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## etc

Interesting pics.

I've had 2 Malkoff M361s and didn't know they had PWM until I was told. It's impossible to see in daily usage due to the high enough frequency that's above human's perceptibility. I forget what the Hz is but it's high. I tried the shower trick to no avail. 

I could only see the PWM in M361 when pointing it at at engine fan inside the engine bay. Actually that was very cool. I have no experience with cheaper lights. I heard Fenix had some in the cheaper models and a lower frequency at that.


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## Hondo

Ahh, the dreaded 100 Hz L0D! See my post #115 for that one in action. The only lights I have ever had that were that bad are the Photon Freedom, which is so cool otherwise, it gets a pass, and my Firefly III. That used the Flupic driver - I should someday try replacing that, and put in a 219 to replace the Lux III LED. But in its day, that thing was amazing, and I never even noticed the PWM. Just thought it was incredible to be able to program the levels I wanted.


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## maglite mike

Do maglites and malkoffs have pwm on lower settings?


----------



## Rattlebars

Motorcycle heated clothing makers have been using PWM since the turn of the century (this one  ). I have used a PWM to power my homemade heated pants and a CC control for the homemade heated grips.

>CLICK ME<


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## xevious

Looks like the OP post #1 images were all made with "http", so with "https" now required they don't display.
I've retrieved them and reloaded, so they can now be seen easily:

Battery with unlimited charge:





Introduce PWM:





25% of the maximum, PWM input





LOWER FREQUENCY PWM:





HIGHER FREQUENCY PWM:






Visible effect of PWM:





hold it so you can see the light on the side of the reflector as such:





wave it sideways like this:





Bad PWM:





Good PWM:





Zoom in, Good PWM:


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## wweiss

Very nice photo illustration of this effect!


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## jeff51

*Great thread!* Spreading PWM awareness is a good thing.

Trying to find info on LED flicker or PWM – The searches bring up a lot of info aimed at gamers and LED refresh rates. These (I think) are not really applicable to flashlight LEDs.

While researching this I can across this article in Nature:
*“Humans perceive flicker artifacts at 500Hz“*
https://www.nature.com/articles/srep07861

Interesting reading - And the reference section sends one down a rabbit hole of other studies.

On another note, some time ago a study found that some air force pilots could identify the type of aircraft from an image flashed on a black screen for 1/250 of a second.
I have seen other references to this, so I assume it’s a real fact as opposed to an internet fact.

*Detecting PWM by Ear*
Most flashlight PWM takes place in the audio frequencies.
A novel way to detect (some) PWM is to hook a PV cell (Solar cell) to a speaker.
Or better still the input of an old powered computer speaker.

If someone has mentioned this before, my apologies I must have missed it in this thread.

Don’t use anything nice or with any real output power. Bad things could happen if too much DC voltage gets pushed at the speaker.
Placing a 100 Ohm to 5K Ohm resistor in parallel with the PV cell will help remove the offset DC voltage and protect the speakers’ electronics.

*PV Cell I got for $3 someplace years ago*





*Computer Speaker - leftover from the Win 98 era.*





Start with the volume control off and a florescent overhead light or a florescent desk lamp a good distance away. Turn on the speaker and increase the volume until you hear a low frequency tone. 

That’s the light singing at 120Hz. Now turn off the room lights and fire up a LED with a known PWM. Listing to it sing.
Always start with the light pointed away from the PV cell to avoid over driving the speakers input.

Those with young ears should be able to detect PWMs in the 16KHz range up to maybe 19KHz range (for those with K9 genes).

Here is a video I made showing some different PWM frequencies and the lights ramping through the
PWM duty cycle. This leads to the video hosted on Flickr.
You can hear the lights sing at their PWM frequency. Start with the volume turned down – just in case.
The top window is the PWM Waveform.
The bottom is a Frequency Spectrum of the light.
Click to watch the video.






*What’s happening.*
First a headlamp with a PWM of about 1,2KHz (1200Hz).
The lamp ramps up and down the duty cycle.

Next is a Nitecore TUBE on low with a PWM of 500Hz.
Then the TUBE ramping at 3KHz through the duty cycle.
The TUBE changes it’s PWM to 3KHz (3000Hz) in ramping mode.
The last bit is the TUBE back at 500Hz on low.

*Why Test?*
I got interested in PWM after getting some lights with truly terrible PWM.
Using the finger wave method shows lights with lower PWMs.
The Photo-Wave method works for lights with higher PWMs but fails to detect lights with higher duty cycles or faster PWMs. It also makes my wife stare at me with that expression on her face (you know the one).

These methods don’t show what the frequency of the PWM actually is. I guess one could make a rotating disk spinning at a known speed and calculate the frequency from that. 

Here are the lights in the video.
First a headlamp.



I reviewed here:
https://www.candlepowerforums.com/vb/showthread.php?460232-Review-A-pure-Flood-COB-18650

*PWM on Low
*



This is the light on low 1.2KHz PWM with a short duty cycle.
*
PWM on Medium Ramp*




Ramping up the duty cycle less “off time” is seen.

On high it’s just a white smear. I didn’t take a picture.
The high duty cycle hides the PWM.

*Then my EDC Nitecore TUBE*.




Which has the odd character of using a 500Hz PWM on low, then shifting to a 3000Hz PWM while ramping.
Clicking to high mode, there is no PWM.

*TUBE on low*




On low at 500Hz it’s easy to see the PWM


*TUBE On low Ramp*




At 3KHz you can still make out the PWM


*TUBE High Ramp*



It’s getting harder to make out the PWM with the longer duty cycle.


*How visible is the PWM?*
I find the key issue for me is related to the time the light spends in the off portion of the PWM cycle.





I got this camping lantern off Amazon. It has a PWM of 100Hz (yes really 0.1KHz).
On high the duty cycle is nearly 100%. And I don’t notice or am I bothered by the PWM.
I used the PV cell mentioned above and my ancient CRT Oscilloscope to look at the PWM.

*Scope at High*.




There is almost no off time during the duty cycle.


On Medium, with the same PWM Frequency, it is truly nasty.
*Scope at Med.*






On low – Good God, this is full on seizure mode.
*Scope on Low.*




Does no one ever look at these things before they go to production?

*Here is the Sofirn BLF SP36*




On Moonlight it has about a 4.8KHz PWM with a very low duty cycle.
*SP69 Moonlight*




I can make out the PWM in the photo


The SP36 switches to a 16KHz PWM while ramping
*SP36 Rampin*g




I can’t detect any PWM in the photo. I guess I can’t more my arm fast enough.

I have several lights with PWMs in the 1K to 3K region. I can tell there is a PWM but it doesn’t bother me even at lower duty cycles.

*Measuring PWM*
I decided to see what I could do to measure PWM without spending any significant amount of $$ or needing special test equipment.
This lead me down a path of testing sensors and software packages to see what I could find that anyone with an interest in this could duplicate.

I think it would be better to branch off of this thread and start a new one since it is fairly involved. 
It will take me a bit to put it together.
Perhaps the OP and the more experienced members could comment on this?

All the Best,
Jeff


----------



## archimedes

Waiting for feedback from @jon_slider ...


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## peter yetman

I'll shine the Batsignal at the clouds. Zero PWM, by the way.
He'll be here soon........
P


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## jon_slider

jeff51 said:


> I have several lights with PWMs in the 1K to 3K region. I can tell there is a PWM but it doesn’t bother me even at lower duty cycles.



Outstanding post! Great photos and info, make it a sticky.. LOL

I agree with your "doesnt bother me" standard of 500Hz from your Tube. Similar to the "not visible in actual use" standard. Others use the terms Good PWM (the kind they dont notice), and Bad PWM (the kind they Do notice). Different people have different degrees of awareness.

the "500Hz doesnt bother me" standard makes a lot more lights fair game 
I mostly did not notice the 467Hz PWM in my HDS during actual use.

I cant recall the last time I saw a post from a Malkoff user about the 312Hz PWM. 
I do see posts from people that notice the 200Hz PWM of the Maratac AA.

I do think it is interesting to know how fast a light is flickering and would like to watch your video. (it requires a log in, please use Youtube)


a couple NoPWM examples
atm Im carrying a SteplessInfiniteRotary w NoPWM and I cannot see the constant current flicker in actual use, even though I can photograph it. 

For a NoPWM AAA light Im a fan of the Lumintop Tool and Maratac, post 2015 when the PWM circuit was abandoned.

can you confirm that your audio device cannot hear those lights sing a PWM song? And does your device also detect constant current flicker that can be photographed, but is not technically PWM?


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## jeff51

John, 
Thanks for the kind words. I'm new to the posting videos stuff, This is my first ever screen capture video and attempt to publish it. (It only took me 5 tries to get linking a simple photo right on the CPF).

The video link leads to a public Flicker page. It plays for me off of an android tablet and a couple of PCs with Firefox or Edge without asking for a login.
Weird. Supposed anybody should be able to watch it.

Is anyone else having problems watching the video?

I don't have a youtube account. I'll see if I can set one up.

The soundcard I used to make the A to D for the software is indeed capturing the audio and that's what is driving the audio portion of the video (that you can't see or hear!).

Some of the current controlled lights can show the ripple voltages sitting on top of the DC offset. It depends how fast the oscillation is.
I'll post a few pics after I get to work later today.

I think I will go ahead and make a branching thread to show what I've found out about doing this on the cheap.
It's easy to do, just there are bunch of "You can use this BUT...…" that needs to be covered.
And (as you can tell) I tend to be long winded when writing stuff.
All the Best,
Jeff


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## xevious

Jeff, thanks for bumping this old topic and refreshing it with new material. Great stuff! :twothumbs

The only light I use these days that has noticeable PWM is a RovyVon Aurora A8. If I'm using it alone, not any other lights for a good long while, the PWM doesn't bother me all that much. But right after using lights with no visible PWM, the A8 is *annoying* as heck on the first 2 modes. It's otherwise a terrific light. I just avoid using low modes for long periods. I'm waiting to hear back from Ken if he'll have a V2 of the A8 out in the fall with no visible PWM.


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## jeff51

Here are some shots of a light with faster PWM.

These images were captured off the setup I’ll be referring to when I get off my butt and put together the post about measuring PWM. This setup is AC coupled and it’s hard to tell if something is pushing a DC voltage.
Since this light is faster I used a linear scale on the frequency plot.

Jon, here is a type of light I think you were referring to.
Rayovac (2) AA “Indestructible” and it is pretty darned tough.

*Rayovac AA on Left, Rayovac AAA Headlamp on Right*




*Rayovac on Low*




Looks to be running a 12.5KHz PWM.
I believe this is a true PWM. When looking at it on a real scope with DC coupling - the off cycle is at 0 Volts.
Those with good ears might pick this up.

*Rayovac AA on Low Close Up*



This is what that waveform looks like on a CRT O-Scope.


*Rayovac on High*




At first I thought it was a 62.3KHz PWM (?).
If you can hear this there are bat research scientists who need your help.
I got a little smarter and now believe this is a ripple caused by the boost circuit.
On a real O-Scope with DC coupling there is a DC offset that the wave rides on.
The ripple is caused by the oscillator frequency? (that’s more of a question – than a statement).

I’m fairly clueless as to what actually is going on inside a driver. This site has helps with that if you find the right threads.

Here is (sort of) an illustration of the ripple riding a wave.

*Office 120Hz + Tube 3KHz*




The main wave are the overhead office lights putting out an ugly sinewave at 120Hz.
The Nitecore TUBE running a low duty cycle at 3KHz is also shining on the sensor. That is the secondary peak at 3K seen on the frequency spectrum.
This sum of signals is what some lights that are running constant current are doing. Except that instead of the 120Hz sinewave, there ripple is sitting on top of a DC offset.


For those who can’t see the video here is a shot of the Nitecore TUBE from my previous post.

*TUBE at 500Hz on Low*




It has a very short duty cycle as see in the phots in the previous post.
The Frequency scale is logarithmic.
You can see the harmonics running up the Freq. band indicating a really good square wave.

*TUBE Medium Ramp*




Here is the shift to 3KHz PWM. It’s running about a 50% duty cycle. This puts this light in the "Good" PWM range (at least for me).
I need to run some sort of tests to see where the PWM Frequency and Duty Cycle start to bug me.
The frequency scale is linear so you see harmonics running up at even intervals.

Just curious, are others not able to see the video in my first post?
Seems like it should work
I will try to get set up with YouTube though.

All the Best,
Jeff


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## peter yetman

I can see the video, Jeff.
I'm on an old OSX and an old version of Firefox.
P


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## jon_slider

I agree 3000Hz PWM falls in the "good pwm" (invisible) range



peter yetman said:


> I can see the video, Jeff.
> I'm on an old OSX and an old version of Firefox.
> P



I am old OSX w Firefox too
when I go to the video link hosted on flicker I get this:





followed by this:




at which point I throw up my hands in distaste

flickr is just trying to make my life difficult..
Im guessing the only people that can see the video, have acceeded to the latest flicker password reorganization, and are logged in to their flickr account

the video does not seem available to mere plebeians
Im either a special case, or non compliant

from which I infer Peter must be presently up to date with a new password and must have a flickr acct, and must be logged in to it, to watch the video

so yeah
youtube please..


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## Modernflame

jon_slider said:


> the video does not seem available to mere plebeians...



I've understood about 10% of this, which puts me squarely in the plebeian camp. Fast PWM = good. Slow PWM = bad. That's about as far as I've gotten. Thank you, gentlemen, for tolerating the educational variety among you.

Cheers.


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## KITROBASKIN

Thanks Jeff!
The originator of this thread has not logged in for about 3 years. This seems like a good place for your posts (if you ask me) but please put a link here to any thread you start that pertains to the information already presented.


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## jeff51

Jon & CLF’ers (is that a word?)
*Got a Youtube channel setup*.
It’s ugly (like me) I need to do some learning to make it nicer.
The Audio is only on the left channel.

WARNING - Turn the volume down - screechy sounds in these videos.
The Videos:
This is the original Low Res Flicker video showing the Super Tiger headlamp and the Nitecore TUBE.





This the HD version of the headlamp.



And here is the Rayovac screaming at 12K and 64K.



Let me know if any of you have trouble seeing these.
All the Best,
Jeff


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## jeff51

KITROBASKIN
Will do. For the shorter stuff, I’ll put it here.
I’d like to do some better videos showing the light as it’s ramping and the waveforms it’s using to control the brightness. I just need to figure out how to do it (!).

The post about making a setup to do the measuring will be pretty long. So I was thinking it might be better to branch off and do it separately.

All the Best,
Jeff


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## jon_slider

jeff51 said:


> The Videos:
> This is the original Low Res Flicker video showing the Super Tiger headlamp and the Nitecore TUBE.
> https://youtu.be/RyJUbe-foPM
> 
> This the HD version of the headlamp.
> https://youtu.be/vlqVixQZgFs
> 
> And here is the Rayovac screaming at 12K and 64K.
> https://youtu.be/V4otzemA744



I see them all, and the first two hurt my ears

I can't hear the Rayovac.. yay!

thanks for showing me another reason to avoid PWM
making plans NOT to listen to that noise again, 
it makes me hostile.. LOL


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## peter yetman

Sounds like a cool white light with PWM might send me over the edge.
P


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## jeff51

None of the lights, luckily, make any physical noise. A headlamp would be especially annoying if it started singing.
The cheap camping lantern dose make a little bit of noise but I have to hold it up to my ear to hear anything.

I have read that some folks do have lights that they can hear and it annoys them.
I wonder if it is poor design or perhaps improper component specs that contribute to singing lights?

All the best,
Jeff


----------



## peter yetman

I did my first the other day.
Did you use the "insert video" button, top right in the toolbar on the Quick reply Editor? You click this and enter the URL.
When you get back to the editoir it should show your URL with VIDEO in square brackets either end of the URL.
Post Quick Reply and you should see a picture box with your video in it.
I think that's about it.
P


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## jeff51

Peter, Thanks, that was the trick I needed.


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## archimedes

jeff51 said:


> None of the lights, luckily, make any physical noise....
> 
> I have read that some folks do have lights that they can hear and it annoys them.
> I wonder if it is poor design or perhaps improper component specs that contribute to singing lights? ....



Usually called "inductor whine" ...

https://en.m.wikipedia.org/wiki/Electromagnetically_excited_acoustic_noise_and_vibration


----------



## xevious

The only flashlight I still have where it's possible to hear inductor whine is on the NovaTac 120P, when running in a low enough mode to trigger PWM. But it's so incredibly faint to my ears, I'd only hear it if I kept the light within an inch of my right ear (_left ear is somewhat damaged and tinnitus cancels out a lot of frequencies_). Anything beyond that would annoy me. At this day & age of LED flashlight technology, it's pretty unacceptable for a maker to produce a light with audible noise or PWM. Just doesn't have to be that way, as so many makers have successfully avoided those unwanted pitfalls.


----------



## jon_slider




----------



## Hondo

I'm guessing you have "circuit warble" in your Mini. But it is a bit fast, or your swing a bit slow, to be certain. I was not aware of any other 4Sevens lights besides some of the high voltage Quark heads having this.


----------



## jon_slider

I actually see dots when I swing the FourSeevens light, but the camera sees the blur I posted. 

I know it is not PWM, the light uses Constant Current, or as I like to call it, Constant Flicker.. LOL

I did swing the Q123 as fast as I possibly could, in an attempt to get a photo that showed the dots that I see with my eyes, but what you see is what my iPhone captured.

My HDS produced dots when I waved it fast, I believe it IS using true PWM.. Though HDS claims they use a type of circuit they call Constant Power, yet another variant in the range of circuits that produce flicker.

My Olights also show blurred dots, like the Foursevens (maybe because Olight makes FourSevens branded lights)...

----
moving on past the Quarks..

An example of PWM from this post:


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## jeff51

I just posted a way too long thread about using a computer and sound card to measure PWM.
Good night time reading for those needing to nodd off...

[FONT=Verdana,Arial,Tahoma,Calibri,Geneva,sans-serif]https://www.candlepowerforums.com/vb/showthread.php?461093-Measure-PWM-using-a-Computer&p=5330349#post5330349

All the Best,
Jeff
[/FONT]


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## DoctorMemory

> Tons of newer cars have LED’s for daylights and rear position lights. As we all know the very same rear position lights are often also used as brake lights, so these lights need to be dimmed to differentiate from when a driver applies the brakes. Some manufacturers –perhaps most?- use PWM to achieve this, but some of them use a very (or failry) low frequency of PWM that actually affects some people, like me. I believe there is a more and more urgent need to sensitise manufacturers as the effects can be very uncomfortable for the eyes of some people. Just as an example, when I drive at night behind some models of Cadillacs or Volvo’s, I either slow down drastically to let them out of my sight or pass them as fast as reasonable (sometimes over the local speed tolerance) because it tires my eyes badly.



I couldn't agree more. Thought I might be the only one that saw dashed red lines for taillights when moving my head.


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## Slideleft

The images are not appearing for me in the original post. Ideas?


----------



## jtmurphree

Good write uup on 
PWM


----------



## Kerisun

Whoa! Thanks a million! I definitely didn't expect that one


----------



## Kerisun

Are there ANY home LED lighting systems you know of that don't use Pulses?


----------



## bigburly912

Kerisun said:


> Are there ANY home LED lighting systems you know of that don't use Pulses?



Every single light that I’ve tried at home and every light we had at Lowe’s 3 years ago used PWM. : (


----------



## JustAnOldFashionedLEDGuy

bigburly912 said:


> Every single light that I’ve tried at home and every light we had at Lowe’s 3 years ago used PWM. : (



No they did not use PWM. Not one. They simply had 120Hz line ripple.


----------



## jon_slider

JustAnOldFashionedLEDGuy said:


> No they did not use PWM. Not one. They simply had 120Hz line ripple.


can you help explain the difference between PWM and Ripple, in practical terms?

1. does ripple create banding in photos, the way PWM does

2. does ripple cause visual trailing dots, when moving ones head... as happens with LED tail lights?


----------



## JustAnOldFashionedLEDGuy

jon_slider said:


> can you help explain the difference between PWM and Ripple, in practical terms?
> 
> 1. does ripple create banding in photos, the way PWM does
> 
> 2. does ripple cause visual trailing dots, when moving ones head... as happens with LED tail lights?



Ripple is due to simple architectures for the driver and trade-offs on capacitor size. By typical regulation in North America, the ripple depth is <30%. As your eye responds to a power law, this is not really noticeable, except when you have some significant motion. It can create banding in photos, but the dark spots are just not a bright, not black. Trailing dots would not really happen, especially since you are not looking directly at the light source like say tail lights. Fixed light sources, don't move either.

With PWM, you have intentional on/off with 100% and then 0%. In a flashlight you have a moving source which makes the impact far worse.


----------



## glideher

PWM is also used in radio controlled receivers e.g airplanes and such as this full range translates to a range of 1194μs which when applied to a PWM servo signal equals 903μs to 2097μs, PWM_OUT - the pulse length that is output to the servo or motor in μs.
same concept as PWM in flash lights, just different application


----------

