Effects of Early Bright, Late Bright and Dim Illumination upon Circadian Neuroendocrine, Electrophysiological and Behavioral Responses
Final rept. May 1991-May 1992,
NORTHERN ARIZONA UNIV FLAGSTAFF COLL OF HEALTH PROFESSIONS
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This study assessed the effects of bright light on biological and behavioral measures to determine if bright light can reduce fatigue and enhance human work performance. Female subjects N37 were exposed to one of 3 lighting conditions in a between groups research design. Subjects in the bright light groups were exposed to 5000 lux white light from 1800 hrs to 2400 hrs Early Bright or from 2400-0600 hrs Late Bright from 1800-0600 hrs Dim Red. Blood sample were taken every 90 minutes. Repeated measures ANOVA indicated a significant interaction effect light x time for tympanic temperature, F3. 339, p.001. The bright light conditions maintained higher tympanic temperatures from 2300 hrs through 0400 hrs. Plasma melatonin measures indicated a main effects difference of F4.009, p.029. Most importantly, the results showed that the light x time of night interaction for melatonin was significant at F59.436, p.000. The suppression of plasma melatonin was greatest from 2230 hrs through 0500 hrs in the Early Bright and Late Bright groups. Cortisol was not affected by the ambient lighting conditions. Dim red light resulted in higher scores on the Stanford Sleep Scale from 2400 hrs through 0500 hrs light x time, F 2.595, p.023. Subjects under the bright light conditions performed better on the cognitive measures of Code Substitution accuracy F3.918, p.030 and Column Addition accuracy F4.660, p.017. These data show some improvements in cognitive performance and alertness associated with bright light exposure and occur with changes in tympanic temperature and plasma melatonin at critical time periods.