# What percent lumen increase to be noticeable?



## Bolster (Apr 20, 2011)

I've forgotten...what's the rule of thumb regarding the percent increase of lumen generally required for a noticeable difference? 

So if you wanted noticeably and unambiguously brighter than 100 lumen, it would have to be what, 150 lumen? 

And to be perceived as twice as bright...what then?


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## vtunderground (Apr 20, 2011)

It's my understanding that 2x lumens is required for a noticeable difference, and 4x lumens for a perceived doubling in brightness.


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## Bolster (Apr 20, 2011)

Aha, good, thank you very much!


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## B0wz3r (Apr 20, 2011)

In order for there to be any noticeable difference in perceived brightness, an increase of only about 10% is sufficient. In order for the perceived increase in brightness to be perceived as 'twice as bright', a tripling of the intensity needs to occur (e.g. 300 lumens from 100 lumens).


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## srfreddy (Apr 20, 2011)

10%....


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## Bolster (Apr 20, 2011)

Can I assume a 10% increase is noticeable when the beams are critically being compared side-to-side? If you saw beams sequentially (one after another) do you think the eye would pick up a 10% difference? 

If you used one light, put it down, picked up another, and it was in reality 10% more lumens, could you confidently say which was brighter?

EDIT: Lumen is singular, lumens is plural? Which is correct to say: the light has 100 lumen, or 100 lumens?


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## srfreddy (Apr 20, 2011)

Actually, I think 20% was the quantity needed to pick one up, use it, pick another up, see it was brighter, IF and ONLY IF it had the same beam pattern. You should really be ceiling bouncing... and this applies to experienced flashaholic with a veteran eye, right? :naughty:


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## gcbryan (Apr 20, 2011)

My understanding is more along the lines of the second poster. Four times for an apparent doubling of the brightness and two times for a significant increase in brightness.

However, I think 25%-50% is noticeable especially when two light sources are compared side-by-side. I don't personally think a 10% increase would be noticeable.

I also think this is only talking about lumen. I would think increases in lux would be more noticeable (I could be wrong here and I don't recall ever reading anything about lux in this regard).


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## tedh (Apr 20, 2011)

Interesting question on the plural of lumen. And it looks like the proper answer, based on the latin root, is...lumina! 

But lumens seems equally acceptable. 

Ted


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## Bolster (Apr 20, 2011)

But "lumina" makes me sound so much more educated and elite!


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## B0wz3r (Apr 21, 2011)

I dislike playing this card because it usually ends up just getting me flamed, but I have a PhD in perceptual psychology and teach sensory perception, cognitive psychology, physiological psychology, etc. in the Cal State university system.

For side by side comparisons, a lower intensity difference can be noticed; for sequential comparisons, it does take a greater intensity difference to be noticeable. 

It's actually more difficult to see differences in brightness in terms of lux (total photons emitted) than it is in terms of lumens (photons per unit area of surface illuminated), for the very reason of how these measures are defined. A given lux will not change based on differences in how the light is columnated, but it will change lumens.

FWIW, "lumina" is the proper Latin plural of lumen... for terms singular terms that end with an 'a' or 'e', the plural form becomes 'ae', such as aureole vs 'aureolae' (pronounced "awr"-"ee"-"oh"-"lee"). (Note that 'aureole' is the term for the 'halo' or holy corona surrounding divine beings, whereas 'areola' is the darker area of flesh surrounding a nipple.)


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## ahorton (Apr 21, 2011)

Great question. I've spent so much time considering this.

My vague results suggest that for a given maximum current, PWM dimming of 3%, 10%, 35%, 100% feel like natural steps when you actually use the thing. I'm not saying it feels linear or logarithmic or anything, just that it feels right.


I set one up at 2%, 12%, 50% and 100% and it really feels like you get great value out of the second mode which is a big step up from the first mode. The 3rd and 4th are brighter, but they don't seem to be worth it. If you turned it on and handed it to me, I couldn't reliably tell you if it was in the 3rd or 4th mode (and I should be able to because I made it!). 

Of course this is all with respect to current levels, not lumens. So 50->100% is a 100% increase in current but only about 65-75% increase in luminous flux.


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## saabluster (Apr 21, 2011)

B0wz3r said:


> It's actually more difficult to see differences in brightness in terms of lux (total photons emitted) than it is in terms of lumens (photons per unit area of surface illuminated), for the very reason of how these measures are defined. A given lux will not change based on differences in how the light is columnated, but it will change lumens.


:thinking:


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## B0wz3r (Apr 21, 2011)

Lumens and defined as luminous flux per unit area; Luminous flux is simply how many photons, regardless of whether they're in a small or large area. Thus, you can two lights with identical lux but different lumen ratings based on how the light throws its beam. One with a narrower (throwier) beam will have a higher lumen count, than one with a wider (floodier) beam.


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## ahorton (Apr 21, 2011)

Just trying to sharpen up a few of those statements so that it's clearer for a newcomer:



B0wz3r said:


> Lumens and defined as luminous flux per unit area;


luminous flux (measured in lumens) = luminous intensity (measured in candela) x steradian (dimensionless)

Think of the steradian as being the area illuminated at 1m. It's the portion (eg, 0.25 or 25%) of a sphere that is illuminated multiplied by 4pi (the total surface area of a sphere of radius 1).

Or if you like:

luminous flux (measured in lumens) = illuminance (measured in lux) x area illuminated (measured in square metres).


A common thing you see mentioned is 'lux at 1m' which is equivalent to candela.




B0wz3r said:


> Luminous flux is simply how many photons, regardless of whether they're in a small or large area. Thus, you can two lights with identical lux but different lumen ratings based on how the light throws its beam. One with a narrower (throwier) beam will have a higher lumen count, than one with a wider (floodier) beam.



The 'throw' is related to the intensity (candela), or if you like, 'the ability to illuminate' (lux). So if they measure the same illuminance (lux), then they must have the same throw.

If they have the same illuminance (lux) but different angles (different areas will be illuminated), the one which illuminates the greater area (wider angle) will have greater luminous flux (lumens)

I think there have been a few typos earlier on and I just wanted to clear them up.


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## saabluster (Apr 21, 2011)

Edit:
What Ahorton said. I really shouldn't post when I'm this tired as I'm far too smarmy as the hours wear on. g'night.


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## B0wz3r (Apr 21, 2011)

A steradian is actually not dimensionless; it is a two dimension measure of angle, most easily understood as a section of a sphere. There are pi radians in a circle, so if you were to cut a circle that was pi radians in diameter out of a sphere, you'd have one steradian. Note too that the size (area) of one steradian is dependent upon the size of the sphere; the larger the sphere (that is, the distance from the center to the surface), the larger the surface area of the steradian, but it still is only one steradian.


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## saabluster (Apr 21, 2011)

BOwz3r you are clearly confused as to what lux and lumens are. Hence the :thinking:. I thought maybe what I posted would give you pause but you came back with more of the same. For instance "a narrower (throwier) beam will" *not necessarily* "have a higher lumen count, than one with a wider (floodier) beam." One does not guarantee the other. This is a common misconception.


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## Bolster (Apr 21, 2011)

OK guys, enough. We can start a different thread on definitions, but my original question has been answered. Thanks to all who contributed.


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