The dreaded duo-pwm and stepdown

tom-

Enlightened
Joined
Jun 10, 2013
Messages
236
In a recent thread an oft lauded niche brand was represented as being immune to pwm, due to the brands superior design/parts/ build and inherently immune to the evil step down (the phenomena apparently is a deliberate manufacturing ploy to misrepresent certain makers lights) due the brands inability to achieve outputs over very low levels relative to the performance of the major players (such as Fenix) manufacturing very high quality-performance and rugged-reliable products.

I do need help in understanding the two issues. I own a light which allegedly is plagued by pwm yet I don't see it-the Mrs. does not see it nor does anyone else who uses the light, whats up with that

With regard to step down; it is stated that with certain lights (those with wacky extreme output levels?) are designed to reach the claimed output for only a brief period of time then reduce in performance to a mere fraction of claimed printed output levels. Additionally, the claim is made that the output reduction is -clearly- shown in charts/graphs- which I am unable to find.

The pwm thing I would very much like to understand, the step down not so much as my interest in lights much over 6k lumens is very very limited though I would like to get some info on the issue.
 

Ozythemandias

Flashlight Enthusiast
Joined
Jan 4, 2017
Messages
1,417
Regarding PWM, different people will have varying sensitivity to it. Maukka and Paramtrek have recently been doing some work in measuring and quantifying noticeable (bothersome) PWM, it's on the other forum though and I don't think we're allowed to link it.

Regarding stepdowns, your question isn't clear to me but even 200 lumen lights have stepdowns. Would you mind rephrasing the question?
 

KITROBASKIN

Flashlight Enthusiast
Joined
Mar 28, 2013
Messages
5,391
Location
New Mexico, USA
Dreaded?
Don't believe everything posted on the Internet. The physics of required step down of high performance flashlights is due to battery and heat dynamics, and sales marketing hype is not your friend. Buyers can become informed by researching. Where? Perhaps a CPF member can give a link...

The Pulse Width Modulation (PWM) issue is more complicated and burdened with perceptions and feelings.
Have you ever seen bicycle enthusiasts go on about components and frame material? Have you seen people get passive-aggressive about telling others what they should or should not get? What about people who are willing and interested in pursuing some aspect that most everyone else is not even aware of, yet want to get others to share their interest and agree it is an issue? Some of us don't like useful flashlights being labeled 'inferior' somehow because it is not 'pure' enough for that particular interest group. And since this is a flashlight forum that many members enjoy reading about all the excellent aspects of portable illumination, it is kind of a 'Debbie Downer' to criticize the specific flashlights that so many people enjoy. Then the cycle of taking offense and justification cranks up again. Candlepowerforums tries to be polite, so some of the things you read here may be fringe, but we are supposed to be polite and therefore don't call-it-out as being not of substance.

As has been said, if you perceive your flashlight flickering when moved quickly, or if you are seeing distracting pulses of light in the rain or snow, get another flashlight of higher quality or more recent manufacture. A blessing and curse of the Internet is the enormous spectrum of opinion and belief, along with the incredible wealth of information.
 

tom-

Enlightened
Joined
Jun 10, 2013
Messages
236
Appreciate the posts. I mistakenly believed that the step down phenomena was particular to very high output lights-perhaps we have not noticed the issue as we rarely keep a light on the highest output for more than 10 minutes or so .

As to to pwm, just how fast does the light have to be moving for this condition to manifest itself? I know we have jogged with the lights on and; nada but what we have not done is wildly swung the light, is this the movement that is required?

PM's most welcome should anyone have info which might be considered 'sensitive' to advertisers here, with the Holidays approaching I will soon be getting a few lights for gifts, Fenix TK75, the latest and greatest, a RC40 and an Acebeam K60.


Ozy, I took away from the posts I have read that the publishing of extreme outputs were only possible with lights that did step down after very brief periods of time, that the practice was purposeful with the intention to deceive

Thanks to all who have taken the time to respond.
 

Modernflame

Flashlight Enthusiast
Joined
Jan 27, 2017
Messages
4,383
Location
Dirty Dirty South
I can't see PWM except in very specific circumstances. Some people report nausea and headaches, but I think this is a very small subset of the general population. Indeed, I stare at computer monitors daily that use PWM with no ill effects. I never knew what PWM was until I read about it on this forum, even though I had used devices that achieve low beam via PWM.

Regarding specific circumstances, I would not want to be caught in the rain using a PWM light. I think I would notice it then.
 

scout24

Flashaholic
Joined
Dec 23, 2008
Messages
8,869
Location
Penn's Woods
There are lights that use a programmed stepdown to meet certain max output runtime numbers on a certain cell. HDS lights are an example of this. Henry has commented here, and on his website, to that effect. His lights are designed around the 123 primary cell fuel source, limiting the amp draw that can be maintained while meeting his runtime goals.
 

tom-

Enlightened
Joined
Jun 10, 2013
Messages
236
It would seem to follow then that the physical size of the light, head/heat sink fins would either eliminate or certainly mitigate this condition-depending of course on what output the maker was attempting to realize?

Are multi led lights more/less or not a factor in step down-all else being equal?-my thinking is that with more you would not have to push a single as hard, less heat?? And regarding the cell type-we as of yet do not have any 18650 batteries only cr123's maybe this is the or part of the reason for the reduction not being an issue???

Who is 'Henry" ????

Thanks for the help.
 

Ozythemandias

Flashlight Enthusiast
Joined
Jan 4, 2017
Messages
1,417
It would seem to follow then that the physical size of the light, head/heat sink fins would either eliminate or certainly mitigate this condition-depending of course on what output the maker was attempting to realize?

Exactly. I understand stepdowns are used for two purposes, primarily to prevent damaging the electronics and lowering efficiency. A larger light run at lower output will not need to step down as much as a smaller light at higher output.

Thermal mass, conductivity of materials used and output are the variables that influence step downs. It's worthwhile to mention that there are also two means of stepdowns, Times stepdowns and actual thermal regulation via a thermistor (thermocouple?).

Timed stepdowns are used frequently, unfortunately. Olight for example only uses these and it sucks. You can buy a copper Olight and an identical titanium Olight and they will both have the same step downs. Obviously this is inefficient because the copper light can handle the heat much better. Same with your example, if you're jogging with a light that uses timed stepdowns, the light isn't taking advantage of the moving air cooling the light.

Proper thermal regulation like Zebralights PID will lower or raise output based on temperature. You can visually see this by running the light until t overheats and output dims, then dunk it in cold water and watch it get brighter.

The ANSI standard for measuring output is to take a measurement at 30 seconds. Very often you'll find manufacturers put the initial step down right after 30 seconds to be able to list the higher number as the claimed lumens.
 

Keitho

Enlightened
Joined
Jun 7, 2017
Messages
781
Location
CO, USA
I'm in the same category as you, tom, I don't see PWM, and just ignore all the posts where people say, "I'll never buy that [whatever], it has 15kHz PWM." As far as step down, there are some manufacturers who deliberately under-drive their LED (or, said in another way, drive them appropriately) to never have to step down due to the LED temp. In my mind, for my use, that is artificially limiting my choice to use brief periods of turbo when I want it. But, if I were in charge of a fire department or a police department or a SAR team, I'd probably opt for one of those under- (appropriately-) driven lights for department issue, to give me one less thing to have to explain to my force.

For me, the type of step down is important. Sometimes, I want my emitters to blast out as much power as they are safely able, given their exact current temperature. So, I look for lights with thermal regulation, as opposed to time-based step down. Time-based step-down will usually keep most LED safe, but I prefer to know that a smart driver is giving me as many lumens as possible when I'm on turbo. Some drivers will step down based on temp., and will automatically step back up when they get cooler (for example, I start riding my bike and cooling my light with all the moving air). That kind of driver is my favorite.
 

Modernflame

Flashlight Enthusiast
Joined
Jan 27, 2017
Messages
4,383
Location
Dirty Dirty South
I'm in the same category as you, tom, I don't see PWM, and just ignore all the posts where people say, "I'll never buy that [whatever], it has 15kHz PWM." As far as step down, there are some manufacturers who deliberately under-drive their LED (or, said in another way, drive them appropriately) to never have to step down due to the LED temp. In my mind, for my use, that is artificially limiting my choice to use brief periods of turbo when I want it. But, if I were in charge of a fire department or a police department or a SAR team, I'd probably opt for one of those under- (appropriately-) driven lights for department issue, to give me one less thing to have to explain to my force.

For me, the type of step down is important. Sometimes, I want my emitters to blast out as much power as they are safely able, given their exact current temperature. So, I look for lights with thermal regulation, as opposed to time-based step down. Time-based step-down will usually keep most LED safe, but I prefer to know that a smart driver is giving me as many lumens as possible when I'm on turbo. Some drivers will step down based on temp., and will automatically step back up when they get cooler (for example, I start riding my bike and cooling my light with all the moving air). That kind of driver is my favorite.

A well reasoned point. I tend to prefer the under driven sort, but I respect this logic.
 

tom-

Enlightened
Joined
Jun 10, 2013
Messages
236
Of the lights I have mentioned for gifts; Fenix TK75 '18-Fenix RC40 and Acebeam K60, best guess on if pwm or step down would be noticed?-don't want to buy duds for presents.

Great info and much appreciate the replies.
 

Ozythemandias

Flashlight Enthusiast
Joined
Jan 4, 2017
Messages
1,417
Of the lights I have mentioned for gifts; Fenix TK75 '18-Fenix RC40 and Acebeam K60, best guess on if pwm or step down would be noticed?-don't want to buy duds for presents.

Great info and much appreciate the replies.

If you're buying it for non-light people I doubt you have anything to worry about. PWM is rarely an issue for non-enthusiasts, I've pointed out terrible PWM and they didn't even see it.

The stepdown is even less of an issue.
 

tom-

Enlightened
Joined
Jun 10, 2013
Messages
236
Definitely for non light people-hopefully a review for the TK75 '18 is coming soon.

Thank you all for the info/interest.
 

jon_slider

Flashlight Enthusiast
Joined
Mar 31, 2015
Messages
5,110
a review for the TK75.

not '18, but its a review:

selfbuilt said:
There is no sign of PWM on any level
...
Runtime testing of the TK75 is slightly complicated by the fact that the light has an automatic step-down after 20 mins runtime. This means that higher capacity batteries will have much longer runtime at the lower levels, as you might expect (e.g. see above).
...
TK75-Restart-18650.gif

...
First thing to notice is that the light eventually steps down to the lower levels, even with repeated restarts. Once the circuit determines battery voltage has dropped low enough, it no longer allows Turbo output. If you try to switch back up to Turbo, it immediately steps down to Hi.
 

ssanasisredna

Enlightened
Joined
Oct 19, 2016
Messages
457
If you're buying it for non-light people I doubt you have anything to worry about. PWM is rarely an issue for non-enthusiasts, I've pointed out terrible PWM and they didn't even see it.

The stepdown is even less of an issue.

How did you know there was "terrible PWM"?
 

ssanasisredna

Enlightened
Joined
Oct 19, 2016
Messages
457
I'm in the same category as you, tom, I don't see PWM, and just ignore all the posts where people say, "I'll never buy that [whatever], it has 15kHz PWM." As far as step down, there are some manufacturers who deliberately under-drive their LED (or, said in another way, drive them appropriately) to never have to step down due to the LED temp. In my mind, for my use, that is artificially limiting my choice to use brief periods of turbo when I want it. But, if I were in charge of a fire department or a police department or a SAR team, I'd probably opt for one of those under- (appropriately-) driven lights for department issue, to give me one less thing to have to explain to my force.

For me, the type of step down is important. Sometimes, I want my emitters to blast out as much power as they are safely able, given their exact current temperature. So, I look for lights with thermal regulation, as opposed to time-based step down. Time-based step-down will usually keep most LED safe, but I prefer to know that a smart driver is giving me as many lumens as possible when I'm on turbo. Some drivers will step down based on temp., and will automatically step back up when they get cooler (for example, I start riding my bike and cooling my light with all the moving air). That kind of driver is my favorite.

It's hard to detect PWM at 1KHz. It's very hard to detect past 2KHz, and almost impossible post 5KHz unless you have rotating equipment and/or set up the conditions for it to be visible (like waving your flashlight really fast during rain .. or in the shower), and even then not easy. That's just detecting it. Biological/health effects at those frequencies? .. no
 

INFRNL

Flashlight Enthusiast
Joined
Feb 7, 2012
Messages
2,971
Location
Bottom Of Pikes Peak
Is the OP (Tom) referring to actual step down of high mode or talking about lights that have the turbo mode?

I will not buy any lights with a turbo mode. I thought this is what Tom was talking about initially when he mentioned having a claimed super high output then a step down to nearly half of the initial output.
This to me definitely sound like a light with a turbo mode. I think these lights are about worthless and I would prefer a light that can handle its high output rating. If a light is rated at 800 lumen for 30-60 seconds then drops to a sustained 400 lumen output; I'd rather just buy a 400 lumen light that could actually handle it. I'm even ok with the gradual step down of the HDS rotary. Just my opinion and i was unclear on what he was asking about on the step down part
 
Last edited:

tom-

Enlightened
Joined
Jun 10, 2013
Messages
236
I didn't think the thread could get more interesting but it has.

Guess I need some help in interpreting the graph, I did believe that the step down phenomena affected only lights that offered a 'turbo' mode and that the highest output would be sustained for whatever the listed time period was, the graph to me shows that the light is decreasing output across the board.

We would purchase a light that offered a step down in turbo mode only depending of course on the length of time that the output was sustained; a few seconds no but a few minutes yes but if and only if the highest non turbo mode was available for very long time relative to the claimed run period.

For our particular needs sustained outputs over 1800 lumens is a liability for trail/backroad use however not having a blast available for a reasonable time is not only also a
liability but it is a liability that could have very serious consequences.
 
Top