Can we really see the difference?

LED Flashlights – General Info
1

Hi all.

The world of flashlights is sometimes similar than the audiophile or wine world. - > Some people pay a lot of money, for “quality” that they cannot feel / identify on a “blind” test (without knowing which one is the cheap and which one is the expensive), but a lot of “experts” recommend.

I have been trying to find some scientific information about vision capacity of the human eye, and how this is affected by the different measures we usually talk about on flashlight forums. But I have not been able to find a post that summarizes all together. CRI, Lumens, and temperature in Kelvin degrees vs human sight limitations.

Are humans able to find differences between a 98CRI and 95CRI light sources? And between a 98CRI and 90CRI? And 98CRI and 80 CRI?

Can human see the difference between 5000K and 4800K light sources? And between 5000K and 4500K?

What about lumens? Is there any difference between 1000 lumens and 900 lumens? And between 1000 and 800 lumens?

How does this change when all this variables start to change?

Can we find differences between a 80 CRI led, that provides 1000 lumens, and a 90 CRI led, with the same lumens? This continues when the 80 CRI led provides only 20 lumens, and the 90 CRI led exactly the same, 20 lumens? Can we find differences between a 80 CRI led, with 4000K tint, and a 90 CRI led, with the same 4000K tint? This continues when the 80 CRI led is 6000K tint, and the 90 CRI led exactly the same, 6000K tint?

Please feel free to include any interesting link of prior topics that speak about this on your comments. Will be always welcome. Let´s see if we can summarize all together!

Thanks in advance, greetings from Germany.

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1. With enough training, you can tell the difference between a 98CRI and a 95CRI light source in a complex scene with lots of varied colors, as long as tint and CCT are exactly the same, but it is rather difficult to do in a normal scene.

98CRI vs 90CRI usually makes for an easier comparison, particularly since of one of the metrics used to average out the CRI metric is R9, which is how good red color rendition is done. Most 90CRI LEDs are 90CRI, but 50 R9, which means anything with red in it will clearly look worse. 90 CRI LEDs with an R9 of 80 are where the comparison gets difficult.

98CRI vs 80CRI is super easy to do.

2. Yes, you can tell the difference between a 5000k vs 4800k light source side by side, and more so if you are used to the CCT emitted by a light(in a 5000k lit environment, telling the difference between 4800k and 5000k is a lot easier).

5000k vs 4500k is pretty easy as well.

3. For lumens, this is where it’s true. To achieve 2x the visible brightness, you need to quadruple the light output, so unless I tried really hard, I doubt I’d be able to tell between 1000 vs 800 lumens, let alone 900 lumens.

4. Well, the brightness might stay the same, but if the CRI goes from 80 to 90, it provides higher light quality, which is always prefered at the same theoritical light output. As long as the other parameters stay the same, higher and better color rendition is always better.

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Your questions are too theoretical for me to try to answer them all.

If you name two specific lights, and ask about their differences, it would be much easier.

fwiw, the word Tint is commonly misused… when you write 4000k Tint, it should actually be called 4000k Color Temperature… Tint is different. Two 4000k LEDs can have totally different Tint.

in any case, for general educational purposes, maybe look through the

Flashlight Wiki

and try to narrow down your questions to specific lights with specific LEDs

4

I don’t think it’s necessary to seek scientific rationalizations for liking good flashlights. Once you own more than two or three lights, you’re no longer buying them for utilitarian reasons, you’re buying them because you enjoy owning and using them. It’s not that expensive a hobby either, compared to, say, liking movies and buying dvd’s regularly.

If you have to look under your bed for some item you dropped, flashlight X might emit the photons you need to find the item, but maybe flashlight Y does that and also makes you happy to use it. That is a description of your psychological state, rather than a measurement of the flashlight’s CRI or luminosity. So it’s more like a reaction to music or poetry than one of light meters. It’s a perfectly good reason to buy flashlight Y instead of flashlight X. If you are getting something out of it and you can afford it, you may as well indulge. Otherwise, focus on something else.

As for the difference between 4500K and 5000K, I think it would be fairly noticeable since it corresponds to a difference of more than 10% in wavelength of the spectral peak. 4800 vs 5000 would be more subtle. Think of the difference between looking at an outdoor scene in the morning vs the late afternoon, or in the autumn rather than the summer. Painters talk about such differences all the time.

For a scientific article with some diagrams and examples, see:

For an older and more naturalistic theory of colors, now understood to be incorrect as a scientific explanation but still considered relevant as a psychological description of color perception, see:

5

And to piss into the already-muddy waters some more, there’s the beam itself.

Reflectors and a crappy emitter can end up with a fried-egg beam, ie, yellower hotspot and bluer spill, or worse, a pissy yellow-brown leaky-yolk corona around the hotspot.

TIRs and/or diffusion film mix the beam better, a TIR lens to preemptively blend the colors, even in a narrow-angle lens, and diffusion film after-the-fact to smear the beam into sheer floody bliss at the expense of any throw.

6

Fascinating thread where the OP is asking questions I have never been able to resolve to my satisfaction. I have many multiples of the same model flashlight with the only difference being the LED and the CRI, and have difficulty seeing a difference in my admittedly unscientific side by side testing. What does seem to make a difference (for me) is color temperature. Perhaps my is issue is my old eyes, Lol.

7

Our eyes and brain do a lot of clever things, so this is a question about individual perception. Go outside and test yourself :slight_smile: .

And report, please.

8

Swapped an lh351d into a zoomie recently. Yes, there is a difference between 70 and 90 cri. Not all the 70cri were equal, xpl-hi was better than sbt90. Lh351d was worse than 219b 4500k, but still acceptable. Once I get an Optisolis build working, I’ll do another comparison.

9

A High CRI LED with pink Tint, improves my psychological state. So does Copper and Titanium… There is also a UI that makes me smile…

so, definitely yes to all the questions :wink:
I can tell, and it matters… to me:
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however, after becoming extremely picky, I am starting to see the pendulum of my obsession with “Retail Therapy”, swing the other way. I am learning to embrace the fleeting happiness of buying Low CRI LEDs, installed in Aluminium hosts, even thought they dont have a Rotary UI, nor pink tint:

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in simple terms
I ran out of perfect grail lights to chase,
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I already have multiples of the ones I like best, along with my choice of LEDs

But rather than stop accumulating, I expanded my acceptable criteria… LOL!
.

.

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“How does this change when all this variables start to change?”
advancing age affects all aspects asymmetrically.

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Hi all, thanks for your answers.

I started this topic, trying to find a source of different links with scientific documents / researchs / studies about the words / vocabulary that we usually read on flashlight forums. Thanks a lot for some of the links already shared, because they contain really interesting information.

Personal opinions are always welcome, but really don´t help very much in my search. I don´t mind if you have a platinum + gold flashlight ,with diamond lenses, because you feel a very big improvement in the light. If you can pay it, I am happy for you (please send me another one for free, so I can test it too $) ).

I also don´t mind if people use your flashlight for professional reasons, or it is just a hobby. If you are happy using flashlights, I am also happy for you. Your reasons are not important at all.

I only want to answer the original question. Can we really see the difference?

I find very interesting some informations that have been already shared:

Tints can be different in leds with the same color temperature, tint depends on the led manufacturing process.

To achieve 2x the visible brightness, you need to quadruple the light output. 1 > 4 > 16 > 64 > 256 > 1024 > 4096 > 16384 ...

CRI is a way of measuring the quality of the color rendering, but maybe it is not the best one, as 2 leds with the same 90 CRI, can make the red color appear different, depending on the R9.

CRI is also different with the led color temperature, a 90 CRI 2700K led can show colors very different than a 90 CRI 4500K led.

I did not wanted to start to "open the pandora box" with other things than affect the light, and could be important for flashlight users, but you are right, Lightbringer, the beam quality is very affected by the optics / reflectors. This needs to be taken in consideration, and there are a lot of differences that everybody can see.

For example, I am reading the topic better low modes with dynamic PWM, I think it is very interesting. But can we really see the difference between a PWM low mode vs a Direct Drive low mode? I am not talking about a light analyser. Of course there are differences. But my eyes can see that difference really?

And also, the last comment of turkeydance, how does aging affect our vision capacity, can a child with 9 years old find differences between a 95 CRI and a 98 CRI led?

Thanks again to all that have commented. Greetings from Germany.

PS: there are many other variables, like efficiency for example. It really makes sense to reduce the battery duration to the half, only to obtain a little bit more of lumens (we already know that 2X visible brightness needs a 4X lumens quantity) and also more heat / more weight in heat dissipation, bigger batteries, etc...? But efficiency can only be measured. We cannot see efficiency with our eyes.

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Do we ‘really know’ that to achieve twice the brightness we need 4X the lumens? Is that really a scientific fact?

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I have read that fact on BLF countless times, and it hasn't been negated by anyone that knows what they're talking about, so I think it's real.

14

For perceived brightness, look up Steven’s Power Law.

The inverse square law you mentioned maps radiation to density at a distance.

15

It’s logarithmic. Twice as bright (100% brighter) looks only about ~31% brighter.

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can you see the differences?:

17

As far as that light placed on the target, no you would be hard pressed to see those difference. However object just in the far peripheral of the spill. A small increase will go from a unidentified to something identifiable.

18

lets try just two extremes:
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now the difference in red and white rings becomes more obvious, right?

photos also dont show as big a difference as in real life.

the best way to learn about LED differences, is to buy and try… photos and text can only hint and point at the real life differences

19

I assumed that the OP in lumen difference was using the same flashlight and LED. Only changing the output as a small change question on what the eye can detect. I believe you may have taken my statement out of context.

20

thank you for pointing out my misunderstanding… you are right…

as to the difference between 800 and 1000 lumens, that is an increase of 25… As a rule of thumb, an increase of 50 is a small but noticeable visual change.

so, imo, a 200 lumen difference is not significant when it is looked at as a percentage of 800 lumens.

info about that +50% perceptibility, comes from the HDS FAQ
“The brightness levels on our flashlights are spaced so that the difference between any adjacent brightness levels appear to be a small but equal change. This visual spacing takes advantage of the logarithmic nature of your eyes to see a huge dynamic range - from very bright midday summer scenes to dim moonlit scenes. Each brightness level is separated by a ratio of 1.5:1 - enough to provide a small but noticeable difference between brightness levels. ”

here is a chart of the mode spacings on HDS lights…
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we can see that the highter levels seem to have larger jumps in lumens, and they do, but the proportion of the jump is +50% for each increase.

the yellow highlighted values are the 4 modes that come as factory clicky presets. Note that the top 3 yellow highlighted modes are spaced at 5x the previous level. These are visually noticeable 5x spacings, in which the brightness appears to be slightly more than double. Based on the premise that it takes 4X the lumens to perceive 2x the brightness.