# Does doubling the lumens double the visible light?



## Font size (Feb 15, 2010)

Is a 150 lumens light 50% brighter than a 100 lumens light? [FONT=&quot]

Does it take more than four times the lumens to double visible light[/FONT]


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## Stevie (Feb 15, 2010)

Yes, with 4 times the output, the range of the light will double and the light will appear twice as bright to the eye.

This is because the perceived light intensity is proportional to the square root of lumen output. So if you double the lumens, the light is only intensified by a factor of square root 2 or 1.41 times as bright. It should also throw 1.41 times further also, as long as you compare the same light with different outputs as the beam angle is very important here. A smaller beam angle will throw farther than a wide beam angle.

If you quadruble the lumens, the light is intensified by a factor of root 4 or twice as much.

I messed about one evening as I was tyring to come up with a formula that would enable me to work out approximate ranges of lights so long as I had the manufacturer specs for the throw at a particular lumen output:

Throw = Lumens x 1335


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## vtunderground (Feb 15, 2010)

A 150 Lumen light will not seem that much brighter than a 100 lumen light. 

A light won't appear to be twice as bright a 2x the lumens... 3x or 4x is more like it.

edit: Stevie beat me too it (and explained it much better!)


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## Swedpat (Feb 15, 2010)

Let me be a bit opposing... I agree with that the actual lumens not (usually) corresponds to the perceived brightness.
According to my experience of several different lights I object against the square root thesis AS AN ALWAYS CURRENT RULE. 
Sometimes I hardly perceive 5 times difference as twice. Other time with other light and brightness I perceive twice the brightness as twice. 
When I compare the 45 and 150lm modes of my Fenix TK20 I always perceive 150lm mode as at least twice as bright as 45lm. With Quark 123/2AA I perceive the 170lm mode as at least twice as bright as 70lm mode.
And my lightmeter confirms the stated differences. 

However, I think it's really a quite subjective issue what we perceive. 

Regards, Patric


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## Ragiska (Feb 15, 2010)

Swedpat said:


> Let me be a bit opposing... I agree with that the actual lumens not (usually) corresponds to the perceived brightness.
> According to my experience of several different lights I object against the square root thesis AS AN ALWAYS CURRENT RULE.
> Sometimes I hardly perceive 5 times difference as twice. Other time with other light and brightness I perceive twice the brightness as twice.
> When I compare the 45 and 150lm modes of my Fenix TK20 I always perceive 150lm mode as at least twice as bright as 45lm. With Quark 123/2AA I perceive the 170lm mode as at least twice as bright as 70lm mode.
> ...



i recommend researching the Weber–Fechner law, and Stevens' power law with respect to visual perception.


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## rickypanecatyl (Feb 15, 2010)

I was so impressed yesterday with an old incandacent mag 3 D light! I hadn't used one in years and my expectations were that it would only be a 1/5 as bright as my EDC 140 lumen light (as my EDC 140 lumen light claims to be 5X brighter!) 
Rather than being only a 1/5 as bright (as surefire would say) I thougth wow! this thing throws farther and lights up a bigger area! My (unnamed) 140 lumen LED lights up a smaller area perhaps 5X as bright but that's not helpful for _*seeing*_ better as much of that light bounces back and blinds me!

Anyone know - is that because my tints are too hot? Would I be able to see better with warmer tints?


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## Casper507 (Feb 15, 2010)

Stevie said:


> Yes, with 4 times the output, the range of the light will double and the light will appear twice as bright to the eye.
> 
> This is because the perceived light intensity is proportional to the square root of lumen output. So if you double the lumens, the light is only intensified by a factor of square root 2 or 1.41 times as bright. It should also throw 1.41 times further also, as long as you compare the same light with different outputs as the beam angle is very important here. A smaller beam angle will throw farther than a wide beam angle.
> 
> ...



I think that was about the same formula I came up with for gestimate conversion when comparing some lights months ago. 

For a better comparison I'd use the Throw = Lumens and consider also the following. 

My M21 will outthrow my MCE drop-in significantly although the lumens are greater from the MCE. From what I've read on this forum at different locations the comparison for throw is LUX. Compare the LUX of the spill and/or hotspot to get an idea of how two dissimilar lights compare for throw. You also need to be comparing readings taken consistantly for distance/equipment. 

Keep in mind you may have other variables if your comparing different flashlights such as the quality of lenses or finish of reflecting surfaces.


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## Swedpat (Feb 15, 2010)

Ragiska said:


> i recommend researching the Weber–Fechner law, and Stevens' power law with respect to visual perception.



What I intented to say is that if I under such situation really perceive a lightsource of 3 times brighter as at least twice as bright I do that. No law can set aside my perception. 
Like if discussing comedy movies. Which is funniest? One person can think that Dumb dumbiest is twice as fun as The naked gun. Other person says it's three times funnier...

Of course NOT TOTALLY the same thing but still we are talking about human perception, which is often subjective related to true technical measuring...and according to my own experience my perception isn't either consistent. I don't know why, but that's it...
Every time I compare my Fenix L1D Q5 between the 12 and 53lm modes I perceive the 53lm mode as MAYBE twice brighter than 12lm mode. Lightmeter confirms the stated percentual difference to be very correct, however. 

Regards, Patric


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## PeaceOfMind (Feb 15, 2010)

Lumens themselves are a linear scale - i.e. twice as many lumens is twice as many photons/twice as much light energy. However as everyone is discussing, you do not perceive it linearly.


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## waddup (Feb 15, 2010)

Swedpat said:


> Like if discussing comedy movies. Which is funniest? One person can think that Dumb dumbiest is twice as fun as The naked gun. Other person says it's three times funnier...
> 
> 
> Regards, Patric



actually, laural and hardy were much funnier then both your movies combined, so you need an sst.


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## Swedpat (Feb 15, 2010)

rickypanecatyl said:


> I was so impressed yesterday with an old incandacent mag 3 D light! I hadn't used one in years and my expectations were that it would only be a 1/5 as bright as my EDC 140 lumen light (as my EDC 140 lumen light claims to be 5X brighter!)
> Rather than being only a 1/5 as bright (as surefire would say) I thougth wow! this thing throws farther and lights up a bigger area! My (unnamed) 140 lumen LED lights up a smaller area perhaps 5X as bright but that's not helpful for _*seeing*_ better as much of that light bounces back and blinds me!
> 
> Anyone know - is that because my tints are too hot? Would I be able to see better with warmer tints?



A statement of a 140lumen flashlight to be 5 times brighter than a Mag 3D surely cannot be fair (a least not with fresh batteries) when 3D is claimed to 76,8 lumens LINK. But when it comes to throw it's another thing. A 200lm thrower can outthrow a 1000lm flood light.
An incan usually is much better for throw than a LED, while LED usually provides a more even illuminated beam with brighter spill.

Regards, Patric


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## Swedpat (Feb 15, 2010)

waddup said:


> actually, laural and hardy were much funnier then both your movies combined, so you need an sst.



Yes, I would like to have one...


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## joema (Feb 15, 2010)

Stevie said:


> Yes, with 4 times the output, the range of the light will double and the light will appear twice as bright to the eye.
> 
> This is because the perceived light intensity is proportional to the square root of lumen output. So if you double the lumens, the light is only intensified by a factor of square root 2 or 1.41 times as bright...


Square root is for a point source, not a typical flashlight beam on a typical surface.

According to Stevens' Power Law (http://en.wikipedia.org/wiki/Stevens'_Power_Law) the *visible* brightness difference is proportional to the quotient of the cube roots of each lumen output. That assumes a 5 degree-wide beam against a flat target in the dark. 

So comparing 150 lumens to 100 lumens:

100^.33 / 150^.33 = 0.875, or the 100 lumen light will appear 87.5% as bright as the 150 lumen light.

A 100 lumen light will visually appear about 63.3% as bright as a 400 lumen light.

Stated another way, a 400 lumen light will visually only appear 1.58 times as bright as a 100 lumen light.

But to generate that 400 lumens requires at least 4x the drive current of an otherwise identical 100 lumen light. Since emitters and batteries are less efficient at high drive levels, the actual cost could be greater than 4x. 

This illustrates why chasing high lumen numbers often produces disappointing results. Upon seeing a new high-output light, people often respond: "it just doesn't look that bright". This is the main reason why.

For those with an HDS, Novatac or Ra light, this illustrates why clicking up one brightness level -- which increases lumen output about 42% -- only appears slightly brighter visually.


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## Swedpat (Feb 15, 2010)

Joema,



> Stated another way, a 400 lumen light will visually only appear 1.58 times as bright as a 100 lumen light


I am still doubtful about some of these statements. When I compare my TK30 with 2xCR123 I really perceive 370lm mode as more than twice as bright as 100lm mode. And I am quite sure other will think that too. Am I unnormal?...
But I will also ask some friends about it how big they think the difference is(without to telling them first of course)... 

Regards, Patric


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## dymonite69 (Feb 15, 2010)

The power law applies to the individual but there are difference between individuals in how 'sensitive' they are to the stimulus.

The bottom line is that perception of brightness (or any sensory stimulation) is not linearly related to the energy of the stimulus (in this case photons).

The exponent for each person lies between 0 and 1. 

Therefore, as you more increasing higher levels of lighting intensity produce less discernible increased in brightness as perceived by the individual.

The analogy is the report of the marathon runner who says that the discomfort of exertion becomes and more uncomfortable until it plateaus. 'The pain doesn't get any worse'. For some that feeling occurs earlier and others later.


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## dymonite69 (Feb 15, 2010)

Importantly the power law demonstrates the law of diminishing returns. 

So what might be appears to be a significant increase in lumens/lux will not be significantly discernible by the user.

Or in another analogy, a car with a big engine is pointless if you can't put the power into the road or the corners.


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## rickypanecatyl (Feb 16, 2010)

I'm just a dummy, and I'm totally guessing here, but I would guess that two flashlights with the same beam ange and if light #2 shines 2X as far and 2X as bright it would have 16X the lumens. 

Since a beam is roughly the same shape as cone and the volume of a cone is 1/3 pi*r2*the height I'm figuring:
A. Flashlight A throws a beam 100 meters with a 40 meter diameter hotspot/corona. It is "lighting up" 41,866 meters cubed.
B. Flashlight B throws the same angle beam 200 meters with a 80 meter diameter hotspot/corona and everything it lights up, it lights up 2X as bright. It is "lighting up" 334,933 meters cubed (8X the volume) 2X as much.
So I'm figuring that to double the beam in every way would then require 16X the lumens ....
does that sound right?


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## Swedpat (Feb 16, 2010)

rickypanecatyl,

I don't think volume shall be included in this matter. What I know twice a throwing length with equal beam profile makes the demand of 4 times lumens.

Regards, Patric


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## VicDiver (Feb 17, 2010)

Interesting, I was just discussing this very same topic at: 
http://www.scubaboard.com/forums/lights/321660-led-lights-few-facts.html

I agree that lightness is not always linear in nature with the HVS, but measurement methods are very inaccurate to make a firm conclusion on any relationship - unless under specific stated conditions with a defined distribution and std dev.

The measurement method will depend on wavelength, exposure duration, scotopic/photopic conditions and whether or not you are looking at the illuminating source or the item being illuminated. If the conditions differ then the results are no longer accurate.

Only thing we can do is measure with non subjective test equipment to evaluate lights and understand that perception of lightness will change in different conditions.

Use the lux meter, it won't lie about intensity  (as long as it is calibrated)


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## Illum (Feb 17, 2010)

lumens is total light output, in the sense of water what your implying is under the assumption with one single spectrum of light and increasing its intensity, it would be the same as opening a valve wider to permit more water to flow through the pipe.

Light exists in multiple frequencies, most of which are invisible to the naked eye...you could have a 100 lumen light with another 100 lumens worth of infrared added on with no direct visual difference


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## VicDiver (Feb 17, 2010)

joema said:


> Square root is for a point source, not a typical flashlight beam on a typical surface.
> 
> According to Stevens' Power Law (http://en.wikipedia.org/wiki/Stevens'_Power_Law) the *visible* brightness difference is proportional to the quotient of the cube roots of each lumen output. That assumes a 5 degree-wide beam against a flat target in the dark.
> 
> ...



You can't use lumens in that formula. That is the wrong unit of measurement. You need cd/m^2


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## VicDiver (Feb 17, 2010)

Illum said:


> lumens is total light output, in the sense of water what your implying is under the assumption with one single spectrum of light and increasing its intensity, it would be the same as opening a valve wider to permit more water to flow through the pipe.
> 
> Light exists in multiple frequencies, most of which are invisible to the naked eye...you could have a 100 lumen light with another 100 lumens worth of infrared added on with no direct visual difference



Nope, IR wavelength won't add to lumens. Lumens take into account the photopic response curve of the HVS.


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## Illum (Feb 17, 2010)

VicDiver said:


> Nope, IR wavelength won't add to lumens. Lumens take into account the photopic response curve of the HVS.



well, maybe that's a bit extreme....say 100 lumen of red won't look like 100 lumens of white:candle:


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## VicDiver (Feb 17, 2010)

Illum said:


> well, maybe that's a bit extreme....say 100 lumen of red won't look like 100 lumens of white:candle:



Sorry, not quite. The response curve takes that into consideration.

See http://en.wikipedia.org/wiki/Candela

If it doesn't make sense I can explain further.


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## bluepilgrim (Feb 17, 2010)

First, just as a lead in, if I want to match a color I can do it pretty well with direct comparison, but I can't do it well at all of I try to remember what a color was, such as staring at the wall and then going to a paint or drapery store --- I always get it wrong. 

Brightness is a bit like that: I can tell fairly well `if two sources are the same brightness with the 'ceiling test', but if I look at one beam next to another, I can say "this is a little brighter" or "this is a lot brighter" but I can't tell you of one is half again brighter, or twice as bright -- or maybe even 3 times as bright. All I can say is 'much' or 'a little' or 'some' brighter or 'about the same'. 

That's similar to judging weight by hand -- I can't give numerical comparisons well -- like saying 'that pole is twice as long as this one'. 

Maybe if I had practice judging `differences with `known ratios I could do better, but I can't tell you that now 'except as a rather rough 'guesstimate' and I would `not be too surprised if I were way off.

(' means corrected error)


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## Cave_Dweller (Feb 17, 2010)

Swedpat said:


> Joema,
> 
> I am still doubtful about some of these statements. When I compare my TK30 with 2xCR123 I really perceive 370lm mode as more than twice as bright as 100lm mode. And I am quite sure other will think that too. Am I unnormal?...
> But I will also ask some friends about it how big they think the difference is(without to telling them first of course)...
> ...



This isn't unusual. Here's a thought experiment...

Go into a completely dark room. Light one candle. How much difference did the one candle make to how "bright" the room appears?

Now go into a room with 10 lighted candles. Light one candle. How much difference did the one candle make to how "bright" the room appears? Repeat for 100 candles, 1000 candles...

In each case you changed the amount of light in the room by "the output of one candle", but the visible effect is very different in each case. (I'm ignoring night apapted vision, rod vs. cone reception and so on... it's for illustration purposes only!).

Also, our eyes are more sensitive to changes in light power at some frequencies than others (same goes for hearing and sound frequencies). Colour is perceptual - in the physical world there are "spectral power distributions". You can make a light appear dimmer or brighter by changing its frequency, while leaving the actual "light power" the same. We humans are non-linear creatures, and all our senses play tricks with us. 

All the best,

Glenn.


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## GMLRS (Feb 17, 2010)

The human eyes Iris has an open to closed factor of 100.

You have to consider it in the calculation.:huh::thumbsup:


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## VicDiver (Feb 17, 2010)

Cave_Dweller said:


> This isn't unusual. Here's a thought experiment...
> 
> Go into a completely dark room. Light one candle. How much difference did the one candle make to how "bright" the room appears?
> 
> ...



Bravo. You're the first one in this thread that "gets" it. I agree fully with your response.

Patric is also right, individual perception trumps all. There is no way an equation is going to tell me what I see or sense. I am the the only one that can do that.


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