Sleep was recorded in congenic F344 albino (c/c) and pigmented (c/+) rats while they were exposed to various light-dark schedules at 10, 50 and 100 lux. In short LD schedules (1:1 and 3:3), both c/c and c/+ rats had similar patterns of NREM and waking in the light and dark. NREM was higher in the light and there was more wakefulness in the dark. These differences were accentuated with increased light intensity. In contrast, substantial effects on REM sleep were seen only in the c/c rats and increased light levels also enhanced these effects. REM sleep in pigmented c/+ rats was virtually unaffected by lighting changes. These results indicate that different systems are involved in regulating sleep-waking and REM sleep responses to light and further that these systems are differentially affected by alleles at (or near) the c locus and/or albinism.