Male albino rats were reared from weaning in 1 of 7 different lighting conditions, then tested with a 2-bar procedure that allowed on and off control of test-chamber lights of 5 intensities for 5 independent test groups. The test session was for 12 consecutive days. After 6 days away from their rearing environment, the differently reared rats continued to perform differently in the same test illumination. Thus being reared in different illuminations not only significantly affected operant rates and duration of self-exposure to various test illuminations, but had a very persistent effect.