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I was watching this video which talks about why violet and idigo in the rainbow can be shown on a computer screen even though the computer screen can not produce light with higher wavelength than blue.

It got me wondering though, brighter and brighter blues are shown on a computer screen as more and more white, which makes sense from a camera perspective in that the colour filters which are used over the ccd to permit coloured pixels wouldn't be perfect and so more of the other colours would filter through making the image white.

When it comes to the human eye though there isn't a filter but a different molecule (Same molecule held by different protein) and so if a particular wavelength is required to activate the molecule, surly much like the gold leaf experiment, the eye can't see more blue when a super bright red is incident on the eye. Can a super bright red look white then?

What would a very intense low frequency (red) light look like?

I was originally going to ask about blue, but the gold leaf experiment analogy doesn't work that way around.

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  • $\begingroup$ If you mean a computer screen, the reddest you can get is x,0,0, where all wavelengths longer than 612 nm are represented by x < 255 and the brightest pure red light is represented by 255,0,0. That's probably a fair approximation of how the eye would see it, too, but that's more biology than physics, since the relevant factor is what cells are doing, not what the light is doing. $\endgroup$
    – g s
    Commented Jun 30, 2021 at 15:23
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    $\begingroup$ At a CSI conference long ago, I saw 1981 Physics co-Nobelist Arthur Schawlow give a plenary lecture. He brought along his ruby laser in a toy pistol housing and fired it at the projection screen. The red was so intense it appeared to me to be white in the center and it visually seemed to ‘peel off’ the screen. Unforgettable! $\endgroup$
    – Ed V
    Commented Sep 30, 2021 at 23:26

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It's possible to briefly experience colors outside the usual color gamut by exploiting after-image effects. There are various options, as explained in the Wikipedia article, Impossible color

Impossible colors are colors that do not appear in ordinary visual functioning. Different color theories suggest different hypothetical colors that humans are incapable of seeing for one reason or another, and fictional colors are routinely created in popular culture. While some such colors have no basis in reality, phenomena such as cone cell fatigue enable colors to be perceived in certain circumstances that would not be otherwise.

Colors that appear more saturated than what your eye can actually detect are called hyperbolic colors.

Here's a simple demo of hyperbolic red. (This site doesn't permit JavaScript, so the demo runs on the SageMathCell server).

Stare at the black dot in the middle of the cyan square for 30 seconds or so, then click it to turn the square red. You may get an impression of a "redder than red" color for a second or two, due to the after-image.

You may get a better result with a different complementary color pair, rather than cyan & red.


Here's a demo of hyperbolic blue. You need to open it in a new tab or window to make it change color.

hyperbolic blue demo

You can play with other hues using my Python script on Github.

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  • $\begingroup$ So if you had a super bright red light would you see a hyperbolic red until the eye adjusted to contract the apature? $\endgroup$
    – jhylands
    Commented Jul 1, 2021 at 8:26
  • $\begingroup$ @jhylands Well, you can't really make a hyperbolic red light. To see hyperbolic red, you first have to "wear out" the cones that aren't very sensitive to red, and then quickly look at red light. That gives your brain the sensation of a color that's "redder than red". $\endgroup$
    – PM 2Ring
    Commented Jul 1, 2021 at 9:28
  • $\begingroup$ However, we don't have simple red, green, and blue sensitive cones in our retinas. There's considerable overlap, especially between the red & green, as this spectrum plot shows. So you can get the strongest hyperbolic effect with blue, using a yellow light that's designed to cover the spectra of the M & L pigments, followed by a blue light that covers the main part of the spectrum of the S pigment. $\endgroup$
    – PM 2Ring
    Commented Jul 1, 2021 at 9:36

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