Evidence shows that pigs have poorer color perception than humans and in particular a reduced sensitivity to the red end of the spectrum. There is little research into the effect of colored lights on pig production. In cases where red light has been used, pigs respond as though in darkness.
Physiology of the porcine eye suggest that the domesticated pig is best adapted for dim levels of natural light. Pig have dichromatic vision, in the pig's eye there are two sets of cones that give the animal peak wavelength sensitivity at 439 nm (blue color) and 556 nm (green color). The photoreceptors in a pig's eye cannot detect the red color (>650 nm).