Answer
Bright light decomposes or bleaches out the visual pigment , rhodopsin, of rods. If one moves from a brightly lit are, to a darker one , for a while one will not be able to see objects distinctly. This will be the case because the cones are not very sensitive, and the rhodopsin will have been greatly reduced in the more light-sensitive rods. If one remains in the dark, vision will slowly improve as the rods reassemble and accumulate rhodopsin. This is usually a slow process, hence dark adaptation takes place slowly.
Work Step by Step
Dark adaptation is the process that takes place when a subject moves from a well-lit area to an area that is much darker. . Cones function very well in bright light, but bright light bleaches out the visual pigment (rhodopsin) of the more sensitive rods.
When one moves from a brightly-lit area to a dimly- lit area, for a while it is difficult to see objects distinctly. This is so because the cones are not very sensitive to low light and the bright liht has bleached the rhodosin of the sensitive rods. However, in the darker area the rods slowly reconsitute and accumulate rhodopsin; usually in 20-30 minutes vision improves and objects begin to stand out. The process of dark adaptation is slow because the processes of re-constitutuition and re-accumulation of rhodopsin in the rods are slow processes and goes on for a long time before there is enough rhodopsin in the rods to enable acceptable acuity.
