The eye shares functions common to a camera. To the left is a diagram of the human eye.
Key components are the cornea, the iris and pupil, the lens, and the retina.
Under contrasting conditions, the eye is capable of seeing a line 2 millimeters wide at a distance of 5 meters. The delta E on the left denotes a change in energy level. On the ordinate, its spectral irradiance reads 2100. For the sea level irradiance curve at the same peak position, the value is estimated to be 1300. Note that at most other spectral locations, the loss is less.