I dont understand why the colored shadow would be causing headache. If for example the lamp would be high CRI but the desk would be actually made of colored material that has the same color, that would not cause headaches, so why it does depend on CRI but not on actual colors of things ?

The same would be then with incandescent (too little blue, all shadows are yellowish), despite 100 CRI....

I think it might at some point be a contributing factor, but not a direct one

They overload the brain:
The brain is used for "normal" shadows, so it is capable to "filter them out" easily without any effort, as these are here billions of years.
But the colored ones pass that "filter", so the brain evaluate them what object they are (if it is thread or so) and only a considerable effort is wasted it came to the conclusion, than they are only shadows. But to get that, the brain had to work harder, so get tired, so the headache...
Similar with flickery light: It first appear as a fast moving object, so potential "danger", so occupy a lot of capacity, again the brain get tired,...

The CRI is not as much important by itself, as the brain is "programmed" to inaccurate eye color perception, it evaluate differences (only when it distort colors so, the normal objects around look too unusual, so start to occupy the brain capacity to evaluate them)

So more natural the lighting, less "false stimuli" occupy the brain, so longer it take to get a headache...

But how can i even see the difference between :

Object with color A lit by low CRI lamp that makes it appear color B

Object made of materials with color B in the 1st place, lit by a high CRI lamp, that makes it appear exactly as it is

And the shadows would be color B of various lower brightness levels in each of those cases

But how can i even see the difference between :

Object with color A lit by low CRI lamp that makes it appear color B

Object made of materials with color B in the 1st place, lit by a high CRI lamp, that makes it appear exactly as it is

The brain tries to figure out what the incoming light is composed of by looking at other objects in the scene, and uses that information to adjust the color perception so that objects always appear to be of the same color. At least, that is what I think after quickly looking at this wikipedia article. This feature was important before artificial lighting, because even in nature, the color temperature varies significantly depending on time of day and the weather.

So in case that the light is high CRI, but actual object colors are "as in low CRI light", there s going to be a problem ?

So in case that the light is high CRI, but actual object colors are "as in low CRI light", there s going to be a problem ?

If all colors appear in such way that the incoming light is composed differently than it actually is, then yes, if I understand it correctly.

(Also, remember that CRI is just one measurement of light quality, two light sources with the same CRI number can have very different light compositions (since color temperature can vary).)

I am trying to imagine this, and i am having hard time to imagine headache etc just as result of looking at objects of various colors. Not saying that it cannot happen

Agree about the CRI part (see my example above incandescen, CRI 100, lack of blue in the spectrum)



I do think of another possibility, in which it would be even more strictly related to CRI : imagine a discontinuous spectrum, in which most of the cells in the eye submit relatively high brightness, but one (with sensitivity exactly in the dark point of the spectrum) submit darkness, ie is sharply inconsistent with the others. Now the brain would think that the eye (this cell) is not ok, and here is where the problem would begin

But then why do outdoor HID light (with spectrum way worse than /765 fluorescent) not have this problem ? (and i used HPS for indoor lighting once, and it did not cause any problem like that either) its kinda contradicting my guess

The eye color sensitivity curves are very wide with quite flat top and even partially overlap (blue with green and green with red), so there is no single "gap" in the visible spectrum.

And for the "colored" shadows, most important is the CCT and color tone (= color coordinates), as shadows are mostly visible on whitish surfaces, what reflect all the spectrum. The shadows on the strongly colored (where the CRI play a role in the color perception) objects are not as distinct, so the CRI alone is not as much important.

It's just my eyes that are messed up