# What is the lumens scale? Twice the lumens equals twice as bright?



## sygyzy

Is it proper to say that a 200 lumen flashlight is twice as bright as a 100 lumen one?


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## Carpenter

Yes it is, but also remember that a 100 lumen light looks the same as a 120 lumen light. I think it takes at least 33-50% more lumems before the human eye can really pick it up.


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## sygyzy

Exactly what I was looking for. Thank you sir. If anyone has anything else to add, feel free.


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## Lighthouse one

DId you check out the Welcome Mat? Lots of answers there for this type of question.


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## StarHalo

For the layman/novice flashaholic:

There are a bunch of different variables that play into "brightness", but keeping it in layman's terms, you can boil it down to the beam profile of the light and percentages.

The beam profile (how the light looks on a white wall) can make a light seem much brighter or dimmer depending on how it's arranged. A good way to visualize this is a garden hose: Let's say you turn on your garden hose spigot to 25%, and holding the hose in your hand you just let the water fall freely from the nozzle. Then you put your thumb over the nozzle - now the pressurized water streams far out and away rapidly. In which instance was there a greater amount of water? The answer is of course that there was the same amount/flow of water for both examples, the spigot was always at 25%, you merely changed how it came out of the nozzle. Conceptually, this works with light also; you can let light flow out broadly in a nearby flood, or you can compact it into a far-throwing narrow stream - the stream can seem brighter to the eye just because it goes farther and/or has a more intense beam profile.

This matters in flashlights because a light that's a "thrower" will always seem brighter than a "flooder". A good example would be if you had a Maglite that was perfectly focused for a nice, intense hotspot. You note how bright this looks on a white wall, then remove the head from the Mag entirely and shine it at the wall again - now the wall is completely dim. In which configuration did the Mag output more lumens? Again, it was the same, the light bulb put out the exact same amount of light for each test.

So now that we know the eye can be easily fooled just by how a flashlight throws light, we must devise a way to gauge *total output*, not just the output in one small area. This test is called ceiling bounce.

When you shine a flashlight at the ceiling of a darkened room, the room as you see it is now lit only by the *total output* of that light - you've removed the element of beam profile and can now see, at least roughly, how much light is being emitted. The test goes something like this; Standing in a pitch black room with two flashlights you want to compare, you shine the first light at the ceiling - you have to shine it in such a way that you can't see the end of the flashlight itself or the beam profile, so pointing it up next to your ear works nicely. Now you're seeing the room lit by the total output of that light. Next, close your eyes, turn off or cover light one and switch to light two, and open your eyes - is the room brighter or dimmer? The answer will reveal which light has more *lumens* regardless of *throw*. (This method works very quickly and decisively when the two lights are more than 20% disparate, below that and you may need to view the room for a full minute or so and then switch lights to catch the tiny discrepancies.)

And speaking of percentages, they're something you have to take into consideration when looking a lumen numbers. Your 220 vs 280 example can be used here - Let's say you're outdoors on a moonless night, and you turn on a 220 lumen light; it will appear very bright and you'll be able to light your way easily. So then you increase your light output to 280 lumens, that's just a little bit brighter, enough that you notice a marginal difference. But here's the kicker - let's say in the same situation, you instead have only a 1 lumen keychain light; on fully-dark adjusted eyes, this is actually "about right" for getting around, and you can navigate fine. But then you increase your light output to 2 lumens, and WOW, that's much brighter, what a difference! Why is 1 vs 2 such a profound difference over 220 vs 280? Percentages - 280 is only 27% brighter than 220, so that's a small difference. But 2 is TWICE/100% over 1, so there's literally twice as much light. Tiny number differences make big perceived differences at the low end of the scale, but not at all on the upper end.


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## sygyzy

Awesome replies guys. The only time I use lumens is when I use it to explain to non-flashaholic friends, in which case I always reference a Mag 3D because I think that's what most people think of when they think of a bright light. I just wanted to be sure I could say "this light is 3x as bright as the Mag cops carry," as an example.


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## Marduke

General rule of thumb is, when all other things are equal, a light must be twice as bright to be "noticeably" brighter, and four times brighter to _appear _twice as bright to the human eye.


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## mudman cj

Here is a thread from a while back that has further discussion on this topic. Marduke's comment applies to light sources that are approximately point sources. For targets in the dark illuminated by a 5 degree beam for example, the ratio is even less favorable, and it takes 8 times more light intensity to be perceived as twice as bright. This is not just a consequence of the inverse square law, but also our vision system. So consider this carefully the next time you choose between an LED that is a little brighter or one that has a tint that provides better visual acuity.


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## ypsifly

Awesome! I just learned a lot. I was wondering about this after I bought an L2D CE and could'nt tell too much difference between the first two settings on a white wall. What I did notice was objects outside of the beam were lit better on the second setting than the first. StarHalo's explanation set me straight.


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## StarHalo

ypsifly said:


> I was wondering about this after I bought an L2D CE and could'nt tell too much difference between the first two settings on a white wall.



A lot of people complain about how "close together" the modes are on various Fenix models, but if you take it outside at night and light something distant, the difference between each mode is profound.


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## Nos

i read that the brightness perception of the eye logarithmical. that means you need 4x the output of a lightsource to see it twice as bright.

short: 4000 lumens are twice as bright as 1000, and 2 lumens are only 1,5x brighter that 1 lumen in total darkness


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## Ilikeshinythings

Nicely put StarHalo & Marduke.

Also consider Lux readings which tell us how far the light throws. A high lumen output and a low lux reading (250 lumens, 5000 lux) will be a bright light with a floody beam-profile, whereas you can have a light with 200 lumens and a lux reading of 18,000 with a more tightly focused beam. Going back to what StarHalo said, the light with 18,000 lux may appear more bright, but the one putting out 250 lumens @ 500 lux is actually giving off more light.


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## Mjolnir

Ilikeshinythings said:


> Nicely put StarHalo & Marduke.
> 
> Also consider Lux readings which tell us how far the light throws. A high lumen output and a low lux reading (250 lumens, 5000 lux) will be a bright light with a floody beam-profile, whereas you can have a light with 200 lumens and a lux reading of 18,000 with a more tightly focused beam. Going back to what StarHalo said, the light with 18,000 lux may appear more bright, but the one putting out 250 lumens @ 500 lux is actually giving off more light.


That's why lumens are really not all that useful in describing output. The amount of lumens a light gives off really do not show how useful it will be at a certain task, since it doesn't take the beam pattern into account. Most of the higher output single die LED lights are all around 200 lumens, so the difference in beam pattern will make a bigger difference than the total amount of light that the LED is actually giving off.
However, if you compare a 3500 lumen HID with an LED, it will appear much brighter no matter what beam pattern it has.


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## Yoda4561

Unfortunately there's no perfect way yet to advertise usable light output. I prefer lumens though, because it tells me how much I'm getting. Light intensity measurements are way more deceptive than lumen output, with tiny little spot-beam lights without any sort of useful output putting out high values. Maybe if manufactuers could standardize on lumens and lux @ 10 meters. I'm pretty satisfied with the current lumens+ flood/spot/focusing arrangement most seem to be using now.


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## Benson

Yoda4561 said:


> Unfortunately there's no perfect way yet to advertise usable light output. I prefer lumens though, because it tells me how much I'm getting. Light intensity measurements are way more deceptive than lumen output, with tiny little spot-beam lights without any sort of useful output putting out high values. Maybe if manufactuers could standardize on lumens and lux @ 10 meters. I'm pretty satisfied with the current lumens+ flood/spot/focusing arrangement most seem to be using now.


My preferred standardization: peak candelas and a beamshot at any stated distance >1m (preferably 3m or greater) with a specified scale (can be as easy as throwing a yardstick in the picture), although where specifying the data in tabular format was essential, the beamshot could be replaced with 50% and 5% diameters (representing, roughly, throw and spill). Spill candelas could, in turn, be estimated from these diameters and throw candela numbers.

Why this, which is noticeably missing total output entirely? It's trivially measurable with one dirt-cheap setup, so no manufacture/distributor can say it's too hard, and it means flashaholics can measure their own tweaked/modded/custom lights on the same basis, and/or verify that lights they buy are honestly rated, without any of the variation and uncertainty associated with homemade ISs or ceiling-bounce tests.


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## ODatsBright

Since lumens and lux are equated, to water, (pressure vs. quantity) why not use a weighted system like multiply the values such as pressure washer ratings, to get a closer handle on actual performance.

Say, something like:

220 lumen light × 18,000 lux = 3,960,000 or scale it to say a light has a CPF rating of 39.6? 

Highly focused beam might look something like this:
80 lumen light × 30,000 lux = 2,400,000 or a 24.0

and a flood beam:
80 lumen × 5000 lux = 400,000 or a 0.04

My 1½¢.


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## Marduke

ODatsBright said:


> Since lumens and lux are equated, to water, (pressure vs. quantity) why not use a weighted system like multiply the values such as pressure washer ratings, to get a closer handle on actual performance.
> 
> Say, something like:
> 
> 220 lumen light × 18,000 lux = 3,960,000 or scale it to say a light has a CPF rating of 39.6?
> 
> Highly focused beam might look something like this:
> 80 lumen light × 30,000 lux = 2,400,000 or a 24.0
> 
> and a flood beam:
> 80 lumen × 5000 lux = 400,000 or a 0.04
> 
> My 1½¢.



And you're back to where you started, with a rating system that only gives you half the story. So a light is "rated" highly. Why?

Having both pieces of information separately, or brightness and beam pattern, is MUCH more useful.


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## StarHalo

ODatsBright said:


> why not use a weighted system like multiply the values such as pressure washer ratings, to get a closer handle on actual performance.



That assumes that lux and lumens are of equal importance to the consumer, which they rarely ever are. It would also give the highest ranking to the flashlight that puts out a ridiculous amount of light into a uselessly narrow beam - as cool as the Maxabeam is, we don't all want to lug one around..

I actually don't value throw that much in an EDC; over time I've found that for most everyday tasks around the house and just walking around outdoors, a broad beam is a lot more useful than a tight thrower beam. Plus I tend to use it on the minimum setting a lot just to preserve night vision, so in many instances, it's neither lux or lumens that are that important. (My EDC on minimum by your scoring system would score a .00076  though the light in my sigline would score 5250 oo


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## ODatsBright

Guess it was my ½¢ worth. LOL

Maybe add beam angle or percentage of lumens that would strike a 2m (human) target size at a given distance, something greater than a meter. Maybe for 'tactical' use, use 100m or even come up with a number that represents a specific amount of light hitting a non reflective object signifying a distance. For example, a rating which would equate to illuminating a human size non reflective target enough for the average person to be able to identify what the object was at X distance. A light which would be able to illuminate such a target at 200m would at least be closer to perceived as twice as 'powerful' as a light with a 100m rating. Making this a 2 part rating with side spill being considered might clarify things too. Maybe like optics, a power rating with a field of view rating. 

I guess that system has it's flaws too, as a 1000 lumen light with a 12° hotspot might not rate better than a 200 lumen light with a concentrated 2° hotspot. Sounds like the only solution is a complex equation which represents all the variables, then you've shot your self in the foot as people making a decision about a light has to understand all the aspects of the rating system. No easy solution.


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## Marduke

ODatsBright said:


> Guess it was my ½¢ worth. LOL
> 
> Maybe add beam angle or percentage of lumens that would strike a 2m (human) target size at a given distance, something greater than a meter. Maybe for 'tactical' use, use 100m or even come up with a number that represents a specific amount of light hitting a non reflective object signifying a distance. For example, a rating which would equate to illuminating a human size non reflective target enough for the average person to be able to identify what the object was at X distance. A light which would be able to illuminate such a target at 200m would at least be closer to perceived as twice as 'powerful' as a light with a 100m rating. Making this a 2 part rating with side spill being considered might clarify things too. Maybe like optics, a power rating with a field of view rating.
> 
> I guess that system has it's flaws too, as a 1000 lumen light with a 12° hotspot might not rate better than a 200 lumen light with a concentrated 2° hotspot. Sounds like the only solution is a complex equation which represents all the variables, then you've shot your self in the foot as people making a decision about a light has to understand all the aspects of the rating system. No easy solution.



But no matter how you rate the equation, what is "good"? Does a score of 5000 mean it's bright and floody, or dim and throwy? 

Sometimes the constituent components tells a better story than anything else.


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## sqchram

I guess I'll pick this thread up since it was the closest to what I'm wondering about and see if someone can point me in the right direction.

Looking at a Zebralight H50, high output at 120 degree flood is 66 lumens, if I were to stick two Zebralights on the headband, head to head - would the output effectively be like a higher-powered 132 lumen, 120-degree-flood headlamp? :shrug:

Oh, and whats a 'GID' when talking about headlamps - the holder?


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## gcbryan

sqchram said:


> I guess I'll pick this thread up since it was the closest to what I'm wondering about and see if someone can point me in the right direction.
> 
> Looking at a Zebralight H50, high output at 120 degree flood is 66 lumens, if I were to stick two Zebralights on the headband, head to head - would the output effectively be like a higher-powered 132 lumen, 120-degree-flood headlamp? :shrug:
> 
> Oh, and whats a 'GID' when talking about headlamps - the holder?



GID= Glow In the Dark.

Yes, regarding two 66 lumen lights being like one 132 lumen light (as far as I know).


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## zipplet

Correct but it wont look twice as bright to you (even though it is) due to how our eyes perceive light.


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## Swedpat

The perception of brightness I have found is tricky and depends on several factors. Sometimes I find that 4 times brightness hardly looks like twice, other time I can think that the twice brightness seems to be twice. But I agree in that the eyes usually don't perceive twice as twice.

According to my experience it will demand at least 30%, often 50% drop of the brightness until I can notice that a the brightness of a light has dropped, when the diminishing is gradually. 
Therefore a light may be considered as practically regulated though the brightness drops 10-20%. You will not notice such a small drop without a side-by-side comparison, and also then the perceived difference is very subtle.

Regards, Patric


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## sqchram

Thanks all.

Yes, I've read a bit about actual brightness vs perceived brightness.

Now entertain this if you would: If I had say 6 x 100 lumen 1 x AA lights with a reflector pattern similar to say the Fenix TK40 - would the overall throw and perceived illumination be the same?

Or are there differences due to say, atmospheric losses where a single (I guess 4 with the TK40), brighter led is more effective than several smaller ones?


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## Swedpat

sqchram said:


> Thanks all.
> 
> Yes, I've read a bit about actual brightness vs perceived brightness.
> 
> Now entertain this if you would: If I had say 6 x 100 lumen 1 x AA lights with a reflector pattern similar to say the Fenix TK40 - would the overall throw and perceived illumination be the same?
> 
> Or are there differences due to say, atmospheric losses where a single (I guess 4 with the TK40), brighter led is more effective than several smaller ones?



I would say yes if the lights are placed together. The beams will melt together and you will perceive it like practically one 600lm light.

Regards, Patric


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## Benson

For the ultimate proof of that concept, see the DB70.


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## C-Beam

Marduke said:


> But no matter how you rate the equation, what is "good"? Does a score of 5000 mean it's bright and floody, or dim and throwy?
> 
> Sometimes the constituent components tells a better story than anything else.



Something like, "A 6 degree hotspot at 3000 lux with a 45 degree spill at 145 lux with a 70 lumen total". Not as succinct as rating system but that's pretty much all the relevant info except for the color.


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## sqchram

Benson said:


> For the ultimate proof of that concept, see the DB70.


 
Ah, I've heard the name be referenced here and there - and now I know! Thanks.


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## c0pasetic

I just found this thread, and it's very informative. I decided to buy a Ray-O-Vac sportsman extreme, mainly because of the 60 hour rating, more than the brightness. I have a tactical light for that. For what it is (and the $21 price tag), it seems sturdy and rather well made imho...except; What I don't get is the difference between 75 lumens on low, and 180 lumens on high. I can't honestly tell much difference, and after reading this thread I am not sure if I should. I get the difference between 1 and 2, but it's a bigger jump between the original math of 220, etc. It's more than twice the lumens, and you have to work to tell that yes it's slightly brighter. I contacted the company and they were happy to take it back, but I don't know enough to know if the light is bad or not. I compared it to some plastic Ray o Vac 70 hour 3 LED lights, and it's noticeably brighter, against the wall, but they were $7 each, lol. If it isn't broken, I have no reason ever to use the high setting (22 hours).
Thanks in advance. (

*runs off to read about the DB light)


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## StarHalo

c0pasetic said:


> What I don't get is the difference between 75 lumens on low, and 180 lumens on high. I can't honestly tell much difference, and after reading this thread I am not sure if I should.


 
You should be able to see the difference between 75 and 180 lumens, the high setting should look like it's at least a half step brighter than the low to unadjusted eyes. The best way to see the difference between two output settings is outdoors at night - walk around with the 75 lumen setting for a while until you're used to it, then kick in the 180 lumen setting, only then will you see that it really is twice as bright..


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## MojaveMoon07

source:
"_Perceived Brightness Index_"
http://www.candlepowerforums.com/vb/showthread.php?271967-Perceived-Brightness-Index


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## Cypher_Aod

i have an XM-L light that has two modes, Max and 10%.

not-particularly-accurate testing shows that the light produces roughly 100 lumens on 10% and 800 lumens on 100%. i can definitely attest that the percieved brightness change from low to high is only a three or four times increase


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## sk8brdkd

is there any way to figure out how many lumens an led flashlight has? i bought a led flashlight that has 51 led's -- it's a very bright flashlight but, am looking to buy a flashlight for a friend and i can't seem to figure out how to differenciate btwn led brightness and lumen brightness -- any ideas?


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## menoceros

You have received many good answers to your question. I would add one more observation, confirming what the other members are telling you.

I have one light that has a variable output from 6 to 145 lumens. As you increase the lumens on this light, it is very noticable at first as you move up from 6 lumens, at about the 80 lumen level, the change becomes less apparent.

This just confirms what the others have said. Going from 80 to 145 is not as dramatic as from 6 to 80.


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## yifu

sk8brdkd said:


> is there any way to figure out how many lumens an led flashlight has? i bought a led flashlight that has 51 led's -- it's a very bright flashlight but, am looking to buy a flashlight for a friend and i can't seem to figure out how to differenciate btwn led brightness and lumen brightness -- any ideas?


A "51 LED" flashlight is most likely using 5mm LEDs. Cheap 5mm LEDs produce around 2-3 lumens while the best ones produce 10 lumens, however 51 premium 5mm LEDs cost quite a bit so i suspect it would be using the cheaper ones, thus it should give about 100 out the front lumens-no very bright for flashoholic standards, since a AAA light produces nearly as much light, and probably better quality light as well.


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## emc.sw.usn.ret

StarHalo said:


> For the layman/novice flashaholic:
> 
> There are a bunch of different variables that play into "brightness", but keeping it in layman's terms, you can boil it down to the beam profile of the light and percentages.
> 
> The beam profile (how the light looks on a white wall) can make a light seem much brighter or dimmer depending on how it's arranged. A good way to visualize this is a garden hose: Let's say you turn on your garden hose spigot to 25%, and holding the hose in your hand you just let the water fall freely from the nozzle. Then you put your thumb over the nozzle - now the pressurized water streams far out and away rapidly. In which instance was there a greater amount of water? The answer is of course that there was the same amount/flow of water for both examples, the spigot was always at 25%, you merely changed how it came out of the nozzle. Conceptually, this works with light also; you can let light flow out broadly in a nearby flood, or you can compact it into a far-throwing narrow stream - the stream can seem brighter to the eye just because it goes farther and/or has a more intense beam profile.
> 
> This matters in flashlights because a light that's a "thrower" will always seem brighter than a "flooder". A good example would be if you had a Maglite that was perfectly focused for a nice, intense hotspot. You note how bright this looks on a white wall, then remove the head from the Mag entirely and shine it at the wall again - now the wall is completely dim. In which configuration did the Mag output more lumens? Again, it was the same, the light bulb put out the exact same amount of light for each test.
> 
> So now that we know the eye can be easily fooled just by how a flashlight throws light, we must devise a way to gauge *total output*, not just the output in one small area. This test is called ceiling bounce.
> 
> When you shine a flashlight at the ceiling of a darkened room, the room as you see it is now lit only by the *total output* of that light - you've removed the element of beam profile and can now see, at least roughly, how much light is being emitted. The test goes something like this; Standing in a pitch black room with two flashlights you want to compare, you shine the first light at the ceiling - you have to shine it in such a way that you can't see the end of the flashlight itself or the beam profile, so pointing it up next to your ear works nicely. Now you're seeing the room lit by the total output of that light. Next, close your eyes, turn off or cover light one and switch to light two, and open your eyes - is the room brighter or dimmer? The answer will reveal which light has more *lumens* regardless of *throw*. (This method works very quickly and decisively when the two lights are more than 20% disparate, below that and you may need to view the room for a full minute or so and then switch lights to catch the tiny discrepancies.)
> 
> And speaking of percentages, they're something you have to take into consideration when looking a lumen numbers. Your 220 vs 280 example can be used here - Let's say you're outdoors on a moonless night, and you turn on a 220 lumen light; it will appear very bright and you'll be able to light your way easily. So then you increase your light output to 280 lumens, that's just a little bit brighter, enough that you notice a marginal difference. But here's the kicker - let's say in the same situation, you instead have only a 1 lumen keychain light; on fully-dark adjusted eyes, this is actually "about right" for getting around, and you can navigate fine. But then you increase your light output to 2 lumens, and WOW, that's much brighter, what a difference! Why is 1 vs 2 such a profound difference over 220 vs 280? Percentages - 280 is only 27% brighter than 220, so that's a small difference. But 2 is TWICE/100% over 1, so there's literally twice as much light. Tiny number differences make big perceived differences at the low end of the scale, but not at all on the upper end.



Thank you for the illuminating (sorry) and fairly brilliant (sorry again) reply to the question. I'm new to the forum but definitely qualify as having a serious flashlight fetish, to put it mildly. I thoroughly enjoyed reading your reply.


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## StarHalo

emc.sw.usn.ret said:


> Thank you for the illuminating (sorry) and fairly brilliant (sorry again) reply to the question. I'm new to the forum but definitely qualify as having a serious flashlight fetish, to put it mildly. I thoroughly enjoyed reading your reply.



Welcome to the party 

Feel free to ask questions, we're here to help.


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