dark adaptation

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The physical and chemical adjustments of the eye, including dilation of the pupil and increased activity of rods in the retina, that make vision possible in relative darkness.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the process of adjusting the eyes to low levels of illumination; cones adapt first; rods continue to adapt for up to four hours