What is Color (stooopid char requirement)

Continuing the discussion from Let's play a Scholarly Game:

Yes…well, a few things (I suspect I am not telling you any thing you don;t already know):

1- Gray, is not, per se, a color…it has no place on the e-m spectrum and no wavelength associated with it. Black (and therefore shades of gray) is the absence of color, i.e. absence of visible spectrum EM radiation.

2 - What is happening as the level of light decrease is that the level of visible spectrum EM radiation is decreasing, not that a color on the spectrum is changing in any meaningful way. If visible spectrum EM radiation of a particular wavelength and amplitude is received by a correctly functioning human eye, it will be perceived as that color associated with that wavelength.

3 - “Green is the last”…interesting, I didn’t know that. But…green is smack dab in the middle of the visible spectrum because our eye developed in a generally green (grasses and leave) world. Just like Eskimos have 1 billion words for snow, the human eye can distinguish man more shades of green than any other color.

Cones (3 types, red, green, and blue centered) and rods must play into this. Cones (used for night vision) are greenish-centered.

I assume the Purkinje shift is behind this. Specifically changes in luminance sensitivity and contrast as the light levels decrease.

Edited: Fixed cone / rod per Luke below. Thanks for catching that, Luke.

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I had forgotten that rods act in triplets sorta like those RGB pixel things in a screen (but reverse)…thanks. You highlight an important point in this discussion…perception vs reality.

Something emitting a specific wavelength, say exactly 530 NM (i.e. “green-green”), is an objective thing. But human eyes/brains might potentially perceive different colors, e.g. if one is moving toward the light at relativistic speeds, or if one has recently taken LSD, or if one is far enough away from light source such that intensity has diminished (diffusion, dispersion, dissipation, whatever) and effects like what you and Rich pointed out come into play. The point being that what color is perceived/processed by the brain might be different for different people as well as different from what was objectively omitted by original source.

For most people, but let’s not forget the tetrachromats: https://en.wikipedia.org/wiki/Tetrachromacy

(another condition is mentioned in there where people claim to see UV light): https://en.wikipedia.org/wiki/Aphakia

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Human eyes have two types of receptors for light. Rods and cones. The cones can see color. The rods can see value (brightness) but not color. The cones are less sensitive than the rods so color perception goes away as the light intensity goes down. This makes it seem like there’s no color in low light like at night. There is color, we just can’t perceive it because it’s not bright enough for the cones to see. Other things like cameras can (old photo of mine lit only by the moon and stars).

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Other way around for rods and cones, but yeah. The rods are sensitive to somewhere between blue and green on the spectrum but they won’t be perceived as that color. They will only be perceived as value (brightness like grayscale). Any perception of color is either coming from the cones or hallucination, like the brain is filling in gaps like it already knows that stop signs are red even if it’s too dark to actually perceive. Our brains are shockingly good filling in the gaps. Gimmicky optical illusions are great evidence of how much isn’t there that our brains are adding all the time.

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I know replying multiple times in uncouth. My bad. Just came across this and wanted to share. It’s a fantastic image illustrating why color vision goes away in the dark. Rods are much larger than cones and more numerous.

Image is from this article.

https://thebrain.mcgill.ca/flash/a/a_02/a_02_m/a_02_m_vis/a_02_m_vis.html

lol…no worries, afaiac. It’s a fascinating subject, actually (when not derailing another thread, that is).

But in the future, please try and be more couth. :–)