Areas V2 and V3 separately process various aspects of vision like shape, color and movement. These areas communicate with other cortical areas including the temporal lobe and the language center. Here we become consciously aware of what we see. Pathways from the LGN also bypass V1, connecting to the brain's motor system, making it possible to sense and react to visual signals without the extra time needed to become consciously aware, this is called blindsight. Other subconscious pathways include the superior colliculi which cause the visual startle reflex to anything unusual.
Astronomers measure brightness in units of magnitude.
The eye roughly follows a logarithmic response, with a magnitude equal to a change in brightness of about 2.5 times. A difference of five magnitudes equals a change of brightness of 100 times. Rod cells are about four magnitudes more sensitive to light than cone cells. Cone cells are concentrated in the very center of the retina, with rod cells reaching a peak concentration at 20 degrees off center and tapering to half their numbers at 60 degrees off center. Interestingly, rod cells are a bit more concentrated towards the nose, than away.