Light And Biology And Culture

[Catalyst]

Hi!

 

I've been wondering for some time now, why are the primary colors the primary colors? What's so special about red and blue and yellow that prevents us from reducing them into other colors? Is it something to do with the physics of light and what the frequencies are? Does it have to do with how our eyes receive the light or how our brain interprets what the eyes see?

 

And relatedly, why do the ends of the visible light spectrum loop onto itself? Red flows into violet and back again, and yet they are on opposites sides of the visible spectrum. This I have to imagine is either a biological effect, or simply that our culture has always done it that way, and so we continue to do it this way.

 

I've read stuff on this site that was similar (and generally over my head), but I wasn't able to find any definite answers. At least, not any answers that fit under my head. Any help would be appreciated as this has been a question loitering in the back of my mind for years.

 

Cheers!

[CraigD]

The primary colors are special because normal human eyes are sensitive to those frequencies of light. They're a biological coincidence, not a special quality of physics.

 

The ends of the visible spectrum don't "loop back onto themselves". Light of higher frequency than Violet is invisible ultraviolet. Light of lower frequency than red is invisible infrared.

 

A few important thing to understand about primary colors - "trichomatic color vision":

• Our color perception doesn't peak sharply at the 3 primary frequencies (colors), but is smeared out over a fairly broad range. See the preceding link for a helpful graph.
  
• It's not necessary for a color display screen, illuminated paint pigments, etc., to emit precisely the same 3 frequencies that our eyes' color receptors peak at. Many different Properly adjusted color displays or selected pigments, while actually emitting very different spectra of light, will be indistinguishable to our eyes.
  
• The color we see is not, in most cases, what is physically there. To see what's actually there, you need a spectoscope.
  

[Catalyst]

The primary colors are special because normal human eyes are sensitive to those frequencies of light. They're a biological coincidence, not a special quality of physics.

 

The ends of the visible spectrum don't "loop back onto themselves". Light of higher frequency than Violet is invisible ultraviolet. Light of lower frequency than red is invisible infrared.

 

A few important thing to understand about primary colors - "trichomatic color vision":

• Our color perception doesn't peak sharply at the 3 primary frequencies (colors), but is smeared out over a fairly broad range. See the preceding link for a helpful graph.
• It's not necessary for a color display screen, illuminated paint pigments, etc., to emit precisely the same 3 frequencies that our eyes' color receptors peak at. Many different Properly adjusted color displays or selected pigments, while actually emitting very different spectra of light, will be indistinguishable to our eyes.
• The color we see is not, in most cases, what is physically there. To see what's actually there, you need a spectoscope.

 

Thank you for your help, that question has been bugging me for a while now! (Most people look at me and tell me what the primary colors are without explanation of why they are.) I didn't know that it's the interactions between the light sensitive cells that produces the experience of color. I always imagined the rods responded to a very limited wavelengths and then fired off (turns out according to Wikipedia that they actually communicate that they have been stimulated by not firing*), and the brain interpreted. Imagine my surprise when a single type of cone could mean either very bright (I'm assuming in amplitude) red or a less intense yellow light.

 

Thank you again!

 

*Wikipedia didn't have a source for that statement. As it seems pretty out of the ordinary for the cells to work that way, I will hold my full trust in abeyance for now. Other than that I have no real objection to the statement so I'll just shut up and go with it