If orange has a frequency in the visible spectrum that is 620nm, how does light that is 2/3 red at 750nm and 1/3 green at 570nm also make orange?
In: Physics
Your eye is full of photoreceptive cells called rods and cones. The rods help you see shapes in low light, while the cones have different receptors to sense color. The cones have three distinct types for sensing red, yellow, and blue light. All your brain can detect is the ratio of these signals coming from each spot in your field of vision, similar to how the pixels on a TV create a color by combining a number between 0 and 255 for each primary color (with 0, 0, 0 being black and 255, 255, 255 being white.)
There’s no receptor for orange. Your brain sees orange when there is roughly equal light absorption by the red and yellow cones and far less by the blue cones. This can be accomplished because the photoreceptors aren’t sensitive to exactly one wavelength, but have a function of sensitivity, with red cones absorbing extremely well at 600nm, but not as effectively at 500 or 700nm. The absorption profiles of the cone cells overlap, with orange light at 575nm triggering both the yellow and red cones. This would create the same effect in the brain as sending pure light of yellow and red in concert (in practice there’s no one wavelength that triggers one type but not the other.)
This chart should help envision what I’m trying to describe:
http://hyperphysics.phy-astr.gsu.edu/hbase/vision/imgvis/colcon.png
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