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Sleep Med. 2013 Jan;14(1):91-7. doi: 10.1016/j.sleep.2012.08.017. Epub 2012 Nov 3.

Exposure to bright light during evening class hours increases alertness among working college students.

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National School of Public Health, FIOCRUZ, 1480 Leopoldo Bulhões St., Office 17, Rio de Janeiro 21041-210, RJ, Brazil.



To evaluate the effects of exposure to bright light on sleepiness during evening hours among college students.


Twenty-seven healthy college students, all males, with ages ranging from 21 to 24years, working during the day and studying in the evening, participated in this study. During the 3week study, the students wore actigraphs and recorded levels of sleepiness. In a crossover design, on the second and third weeks, the students were exposed to bright light (BL) at either 19:00 or 21:00h. Salivary melatonin samples were collected before and after BL exposure. ANOVA test for repeated measurements were performed.


After BL exposure, sleepiness levels were reduced at 20:30 and 22:00h (F=2.2; p<0.05). ANOVA showed statistical differences between time (F=4.84; p=0.04) and between day and time of BL exposure (F=4.24; p=0.05). The results showed effects of melatonin onset at 20:00 and 21:30h and sleepiness levels (F=7.67; p=0.02) and perception of sleepiness and intervention time (F=6.52; p=0.01).


Controlled exposure to BL during evening hours increased alertness among college students. The effects of BL on sleepiness varied according to the time of melatonin onset.

[Indexed for MEDLINE]

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