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Rods are very large and very sensitive to subtle light changes and motion.
Rods are active in low light levels. We call these “scotopic” situations.
Rods populate the periphery of the retina and parts of the macula. The Fovea (center area) of the retina contains no Rods.
There is only one class of rods, and they all contain the same
photopigment. This photopigment is called Rhodopsin and is most sensitive to radiation with a wavelength of 504 Nanometers. This wavelength of radiation would translate to the color experience “blue-green” to normal color vision.
Because all of our rods have the same sensitivity and respond to light the same,
they only translate value information. Thus in low light level, “scotopic”
situations, our rods translate only a judgment of bright or dark to the brain. Scotopic vision situations, therefore, appear monochromatic (one-colored).
Cones
Cones are the photoreceptors that populate the central areas of our eye and are responsible for all of our high detail and color vision functions. Cones are organized into three distinct classes, and each class contains a different chemical photopigment. The different peak sensitivities of the different classes of cones make color distinction possible. Understanding how light is detected by the different types of cones and translated to the brain is necessary to understanding color science and making appropriate light source decisions.
Cones are active in high light levels. We call these “photopic” situations.
Cones populate the central parts of the retina. The macula is primarily made up of cones, and the fovea at the center of our retina is exclusively made up of cones.
Cones are responsible for our color vision and are small in size in order to translate detail.
There are three different classes of cones, each named for the photopigment chemical that it contains. These three photopigments each have a peak sensitivity to a different wavelength of light and are named for the wavelength to which they are most sensitive. These unique sensitivities are what make discerning color possible.