Cone cells, or cones are cells in the retina of the eye which only function in relatively bright light. There are about 6 million in the human eye. _Cone cells are less sensitive to light that the rod cells.
The human eye has three types of color sensors, or cone cells (corresponding to the red, green, and blue) is what lets us reproduce colors at all using just three pigments on paper, or just three phosphors in a monitor.
Thus the "color" of any light can be specified by three numbers (e.g. the photons caught by each cone type).
The first type responds most to light of long wavelengths, peaking in the yellow region; this type is designated L for long.
The second type responds most to light of medium-wavelength, peaking at green, and is abbreviated M for medium.
The third type responds most to short-wavelength light, of a violet color, and is designated S for short.
The three types have peak wavelengths near 564-580 nm, 534-545 nm, and 420-440 nm, respectively. The difference in the signals received from the three cone types allows the brain to perceive all possible colors, through the opponent process of color vision.
