ABSTRACT
The human eye is sensitive to the electromagnetic spectrum between the wavelengths 400 nm (violet) and 700 nm (red), with maximal sensitivity at 550 nm (green). The range of light intensity to which we are exposed is huge, about 1011-fold. Although the eye can respond to a single photon of light, 5-8 photons arriving within a short time are required to give the experience of a flash of light in the dark-adapted state. Because intensity is encoded by the visual system logarithmically, it is difficult to distinguish differences in intensity at high light levels.
