Is It True? Double Lumens Only 25% Incease in Brightness?

jar3ds

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Is this true? From an online article I read they said that if you double the lumen's your eye is only seeing a 25% increase in Brightness?

I used to think that the HDS EDC 42 wasn't very bright... .but is it only 25% less than the U85?

As a side note question... What is the Surefire U2 rated at on its second brightest setting?

Thanks!
 

jtice

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I am not sure about the exact lumen ratings etc.

But it takes alot more than double the power into an led,
to make it twice as bright.

This is mainly due to how our eyes see light.
The brighter it is, the bigger jump in brightness you have to make in order to notice it.

~John
 

Paul_in_Maryland

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When crossing streets during my 28-minute walk between the train station and my job, I make myself visible using a flashlight with a G&P 12V 220-lumen lamp assembly with an orange traffic cone. The orange cone stands out, even in daylight.

Well, today I substituted a 9V 105-lumen lamp assembly. The difference was dramatic. Instead of halting when turning a corner, drivers would keep turning into my intersection. I had to stop in midstreet as car after car ignored my cone...because they didn't see it. A TL-3 (175 lumens) fared little better.

Nighttime is not a problem, but for daylight use, my life deserves 200 lumens. Maybe it does yield only a 25 percent difference, but it's a difference that drivers can see.
 

HarryN

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The basic responses are correct that the eye's perception is non - linear, and sensitive to the color temperature, wavelength mixture, etc.

On the positive side, your eye does not need to double the brightness in order to see better, and you can enhance the effective result by thinking through how your eye works with various light sources and color mixtures.

In Paul's case, you see a dramatic example of how not only brightness, but color content is affecting vision. Part of his challenge is not just the overall brightness, but the color content. He is using a white light which contains some RED / Orange to shine through an orange cone. Most of the light is absorbed by the cone (like a filter) and the R/O part shines through. If he uses a different lamp with a different color temperature distribution for the illumination, the R/ O content can change dramatically, even for similar power, and perhaps even the same Lumen rating.

As an alternative, if he used a lamp which had an output entirely in the Red / Orange region, the overal Lumens rating and power ratings might be substantially lower, but the absorbtion losses due to the cones filtering would be very low. In this case, if he used Lux III R / O, (not sure how many with out calculating it, but maybe even 1), his visibility would improve and power draw would be well under 5 watts, maybe even 1/2 of that.

This example (applied to traffic lights) is the exact reason why LEDs became known for being more efficient than incan bulbs. For monochromatic applications, they are hard to beat, for white - its a more complex answer.
 

lamperich

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since i got my own lux meter i know that you need at least a step of *2 .
The fun beginns with x4...

i think with lumen it´s the same.

More important is:

regulation that can handel the Vf variation!!!!!!
for your application the correct reflector/optic !!!!!(Surefire has a Lux5 torch with only 500 lux.....
grinser2.gif

AND color rendering. (can you say for sure this is that color or do you need to think. eeh that´s mud ?!?)
good cooling is always a good idea.


if your torch do this than you can take a look on a U bin Lux3
drool.gif
 
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Roy

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Reporting runtime as 50% of max brightness is based on the idea that it takes a light change of 50% before the human eye will notice a change in brightness. I really don't know if this is true or not, but it makes a nice reference point for measurng runtime.
 

LightObsession

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Roy said:
Reporting runtime as 50% of max brightness is based on the idea that it takes a light change of 50% before the human eye will notice a change in brightness. I really don't know if this is true or not, but it makes a nice reference point for measurng runtime.

If this is true, then when looking at runtime charts to compare lights, there isn't much advantage to a light with a completely flat curve until it falls out of regulation vs a light that slowly decreases in brightness to 50% because the eye would hardly notice the change in brightness. I suspect that the eye would, however, notice color shifts as overall brightness decreases.

I may have to reevaluate how I was searching for well regulated 2AA lights to include some that I had already eliminated if a flat discharge rate isn't that advantageous as far as the eye is concerned.
 

Paul_in_Maryland

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HarryN said:
If [Paul_in_Maryland] used Lux III R / O, (not sure how many with out calculating it, but maybe even 1), his visibility would improve and power draw would be well under 5 watts, maybe even 1/2 of that.
Boy, did I misunderstand this concept. I assumed that a "cool" light would work better than a "warm" light. So should I forget about using a white 5W LED drop-in?
 

Roy

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The shape of the runtime plot can be a determining factor when evaluating how a light is going to be used. For example, a light with a dead flat plot and a sudden drop in output would not make (IMHO) good light for a LEO or firefighter. Not knowing when a light is about to go out could be dangerous. For my purposes, I want a light a light with a flat plot....but my life doesn't usually depend on wheather a light goes out or not.

A runtime of 50% of max brightness will give you a measure of how long a light will be bright. Just one of many thing to consider when buying a flashlight.
 

greenLED

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Roy said:
Reporting runtime as 50% of max brightness is based on the idea that it takes a light change of 50% before the human eye will notice a change in brightness. I really don't know if this is true or not, but it makes a nice reference point for measurng runtime.

I thought it was 20% change for our eyes to notice; due to the non-linear way our eyes perceive light intensity.
 

HarryN

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Paul_in_Maryland said:
Boy, did I misunderstand this concept. I assumed that a "cool" light would work better than a "warm" light. So should I forget about using a white 5W LED drop-in?

Hi Paul - If the goal is to use the light primarily for your visibility application, then a cool white LED, such as a normal Lux V is really the wrong direction. Usually, LEDs are configured to have a substantially lower RED content than the typical incan light. The notable exception is the 1 watt warm Luxeon.

Slightly off topic, but I am very interested in testing your application with a light I am working on. Would you be willing to test a proto for a week or so (no cost). Of course, you should discontinue use before you are run in to. It would not be ready before January.
 

Pixel

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"Double Lumens Only 25% Incease in Brightness?"

It is not about brightness but about the eye perception. If you look at the overal beam spot it might be true. But if you perform a ceiling bounce test the difernce is by far not so small. I am comparing my mother Q3: Nuwai TM-301X-3, that hopefully outputs 50 lumens and a SF L2 with 100 lumens. The overal room illumination I get with the L2 is more than double in comparision to Q3.
 

lamperich

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i thing iam wrong in my last posting...

i wonder a long time now what the realtionship between lumen vs Lux is.

right now i have a torch with ~400lux
what i know since i got a Luxmeter is that i needs forth of this
that means.. 1600 Lux.

So if every thing is same Reflector,current etc.
what lumen increase is need to reach this goal and is it independing on the focustype?
What i know is that increasing the distance *2 lux decrease /4
and as far as i know it´s indepentend on focus typ.



@ jards
I think our two quesions supplement each other very well or should i open a new thread?
What do you think?
 
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HarryN

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Hi Lamperich - I am sorry to say that the anwer to your question is not entirely simply either, but, in general, yes - 4 x the Lux means you need 4 x the Lumens if the optical characteristics remain constant.

Just slightly more complex - the optical characteristics are hardly ever a constant with this much of a change in the source. Example - if you go from a Lux I to a Lux V to obtain the desired shift - the optical characterstics are quite different. I think similar things are true with incan bulbs, but I am not as familiar with them.

If you need 1600 Lux in a narrow beam, that is not terribly hard to purchase, but 1600 Lux in a broader beam (L4 type broad beam) is definitely substantial power.
 
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