- Photoreceptor cells perform a process known as phototransduction. When photons strike the photoreceptors, the membrane potential in the cell changes appropriate to the charge of the light particle. When this happens, a neurotransmitter particle called glutamate is released. Individual photoreceptors do not detect color, but rather the presence of it. Only multiple cones working in concert can interpret color.
- Rods allow the eye to perceive low light environments accurately. This is referred to as scotopic vision. They don't perceive color and can't perceive space very accurately. They are over 1,000 times more sensitive to light than cones, however, and perceive motion far more effectively. In the human eye, rods require approximately 30 minutes of adjustment to achieve optimum efficiency at any given low light level.
- Cones are responsible for daylight vision, and are specialized by color. Out of the 6 to 7 million cones in the human eye, about 64 percent are green, 32 percent are red and 2 percent are blue, according to a presentation by the Department of Physics at Georgia State University. Colors are accurately perceived by three or more cones firing in concert in response to light stimulus. They adjust to changing light levels far more quickly than rods do.
- Each specialized cone is tuned to interpret light of a certain wavelength. To gain greater accuracy, the eye compares the light readings across multiple cones to form an image in the brain. The eye interprets color mixtures by determining what proportion of the differently colored cones are stimulated. For example, yellow is perceived when red cones are activated in a slightly higher proportion than green cones.
- Damage or loss of rods leads to night blindness, while loss of cones leads to blindness. Disproportionate levels of color cones can lead to color blindness, as the eye in that case makes errors in processing colors accurately. Vitamin A deficiency leads to rod damage and decreased night vision ability.