Color Blindness
Color blindness changes the sensitivity of the eye as a function of wavelength. For people with protanopia, the peak of the eye's response is shifted toward the short-wave part of the spectrum (approximately 540 nm), while for people suffering deuteranopia, there is a slight shift in the peak of the spectrum, to about 560 nm. People with protanopia have essentially no sensitivity to light of wavelengths more than 670 nm.
Most mammals other than primates have the same luminosity function as people with protanopia. This makes it possible to study the nocturnal life of animals by illuminating the scene with long-wavelength red light that they can't see.
For older people with normal color vision, the crystalline lens may become slightly yellow due to cataracts, which moves the maximum of sensitivity to the red part of the spectrum and narrows the range of perceived wavelengths.
Read more about this topic: Luminosity Function
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