Anti-blue light gear. Some claim to filter blue light without changing color perception. Real or fake?

Physics Asked by lostdatum on November 30, 2020

Please note: I do NOT wish to debate here whether blue light is really harmful or not. I just want to discuss what the anti-blue light technologies actually do.

What I found:

Please note: To avoid any mercantile involvement, I’d rather not give any information that would help identity the manufacturers quoted below.

  1. A lens manufacturer (for glasses) declares they master an anti-blue-violet light (UV & HEV) filtering technology. A multi-layer coating is laid over the lens, reflecting incident blue-violet light. They claim: "the lenses are almost completely clear but have a very faint residual tint". NB: another manufacturer with similar technology qualifies it as "interference filtering".

  2. Another lens manufacturer declares they master an anti-blue-violet "absorptive filtering" technology. They claim: "we have also managed to correct the slight residual yellow tint".

  3. A computer monitor vendor claims their anti-blue light screen achieves "over 90% reduction in eye-damaging blue light with little to no effect on display brightness and color".

What I believe:

Please note: I do have a general physics background but I am not an optics specialist, so I do not claim absolute truth.

a) Blocking 100% intensity in the wavelength band associated to blue color implies those wavelengths cannot make their way to your eyes, which implies you cannot see the color filtered, which implies you see only the yellow/green and red parts of the spectrum, which implies that your color perception is indeed altered: everything will look yellowish to reddish.

b) Moreover, since part of the spectrum of incident light is blocked, then total light intensity is reduced which should result in dimmed light perception (unless, of course, if the source spectrum contains no blue light).

My conclusion:

Now regardless of the technology used (reflecting, absorbing, sorcery, voodoo, etc.) and even if only 90% or 50% or whatever intensity is blocked, the effect will be lessened but still, color perception will be altered and everything should look less blue and more yellow-red. And unless intensity loss is compensated (e.g. monitor brightness tuning), it should still make things look dimmer.

So regarding claims in 2) and 3), I am skeptic. What do you think? Any insights are welcome and especially from people with advanced knowledge of optics or color theory.

One Answer

To answer your question, we need to go back to how LCDs work. back-lit lcd The colours in our LCD displays on monitors and laptop screens are generated by pixels (transparent) which are then back-lit using white LED's placed behind a sheet of translucent diffusive layer. Now the problem (probably) lies with these LEDs. These LED's (as is the case even with LASERS) are not strictly producing light in ONLY the desirable part of the spectrum. So there is a bit of spread of intensity in the part of the spectrum where we expect no amplitude, in the case of white LEDs this is : UV side and a bit into the far red side as well.

Prolonged exposure to these UV rays can definitely cause damage to the eyes which is a genuine concern unlike the blue vs yellow light debate. As we know, UV get mostly absorbed in the eye lens, and prolonged exposure can cause cataracts among other issues... ..I guess you already understand this, but what I believe is that as with most unreliable information sources on the internet and elsewhere, they are partly true and partly wrong. They use the true part to hide the flaws, and make use of the general lack of awareness to sell low quality useless products. But some of them might as well be using the term "blue" as a general term for high frequency rays beyond the visual spectrum.

But surely, the claims (2) and (3) (specially the second one) when taken on face value, make no literal sense if they mean what they say...if they blocked out the "blue" (literal blue and not UV), then there is no way to make the yellow tinge go away...because to remove it they'll have to add the blue back which is not possible unless they loose on the brightness at least, and anyways they'll be re-adding the blue that they removed (or much worse, removing yellow thereafter to make it less yellow)!!

So maybe they are trying to sell ordinary cellophane sheets saying that they first absorb the blue (hence they are "filters"!!), and then re-add the blue so that the screen doesn't look bad at the colours, and they found that the only way to do that is to use simple transparent cellophane sheet!!..and hence their product. Absolutely justified! Can't put physicsy doubts to such people, they'll probably prove to you that Einstein was the most foolish person ever born!!

Answered by Crazy Goblin on November 30, 2020

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