Photopic vision is the vision day by opposition scotopic vision is night vision.

     Photopic vision is mainly thanks to cones located on the retina of the eye.

     The sensitivity of the eye in photopic vision is not the same for all wavelengths. The maximum sensitivity of the eye is obtained for a wavelength of 555 nanometers.

     Scotopic vision is the "form" that is peculiar vision in low light conditions. In humans vision scotoptique is mainly provided by the rods of the retina which have an important sensitivity to light (see rhodopsin) but respond to all visible wavelengths (thus giving a perception in black-and - white or panchromatic).

     The maximum sensitivity is achieved in humans after about 45 minutes to stay in the dark which corresponds to the time necessary to regenerate all of rhodopsin molecules in their active form. Due to the distribution of rods on the retina the maximum sensitivity lies not in the optical axis (the fovea consisting solely of cones) but a few degrees of it.

     The sensitivity of the eye in scotopic vision is not the same at all wavelengths. The maximum sensitivity is obtained for a wavelength of 507 nanometers.

     Thanks to the cornea (the transparent envelope of the eye) and iris (which is closing for the determination of quantity of light) an image is formed on the retina. It is composed of small rods and cones.

     The rods forms a pigment so-called rhodopsin, are located at retina periphery, can perceive the brightness and movement (scotopic vision) while the cones situated in an area called fovea can differentiate colors (vision photopic). There are really three kinds of cones :

• a kind for red (570 nm) called erythrolabes

• a kind for green (535 nm) called chlorolabes

• a kind for blue (445 nm) called cyanolabes

     Thus, when a type of cone is missing the color perception is imperfect this is called blindness (or dichromasie). One generally distinguishes individuals with this anomaly by type of cone defective :

• The protanopes are insensitive to red

• The deuteranopes are insensitive to green

• The trinatopes are insensitive to blue

     On the other hand, it is noted that the sensitivity of the human eye to light intensities on the three primary colors is unequal.