Responses of albino and hooded rats to various illumination choices in a six-chambered alleyway.

To determine preferred illumination when multiple choices were simultaneously available, 10 different levels of illuminance (including darkness) were grouped into three overlapping ranges, each composed of six different choices. Subjects were permitted to move freely among six chambers in an enclosed alleyway for 48 continuous hours. Entries and duration in each of the chambers served as the dependent variables. Five groups of seven animals each were tested. Hooded rats preferred darkness, 0.01 ft-c (0.11 lx) and 20 ft-c (215.2 lx) about equally; each albino group preferred the dimmest available illuminated choice, viz., 0.01 ft-c (0.11 lx), 0.1 ft-c (1.08 lx), and 1.0 ft-c (10.76 lx); control rats distributed their time equally among all chambers. Activity of all groups reflected a typical circadian rhythm. These relative preferences for illumination contrast with absolute preference previously reported and perhaps reflect methodological differences.