Evaluation of Bright Light Use to Reduce Sleepiness in Brazilian University Students

*Correspondence author e-mail: lilianeteixeira@ensp.fiocruz.br Introduction: Former studies carried out among young workers have shown high sleepiness levels during evening school attendance. In addition, several studies have shown that exposure to bright light prevents sleepiness during night work. However, as far as we know, the effects of bright light exposure is still unclear during evening hours among college students. Aim: To evaluate the effects of bright light exposure on sleepiness during evening hours among college students. Methodology: Twenty-seven healthy College students, all males, with ages ranging from 21 to 24 years old, working during the day and studying in the evening, participated in this study. During three weeks the students filled out daily activities logs, including sleep duration, wore actigraphs and recorded levels of sleepiness three times in the evening (19:00; 20:30; 22:00) using the Karolinska Sleepiness Scale. In a crossover design, on the second and third weeks, the students were exposed once to white bright light during 20 minutes (8.000 lux) at 19:00h or at 21:00hours. Salivary melatonin samples were collected before and after light exposure. A repeated measure ANOVA was performed to evaluate the effects of light exposure on sleepiness. Melatonin levels (increased or decreased after light exposure) and sleep duration before light exposure (≤6 hours or > 6 hours) were considered as factors. LSD Post Hoc test was used. Results: The percentage of individuals with melatonin suppression compared to baseline after light exposure at 19:00h was 52.2%, and at 21:00h, 57.9%. The results showed a reduced level of sleepiness at 22:00h when bright light exposure was presented at 21:00h (F=4.01; p=0.03); the mean values of sleepiness at 19:00h were 4.17 ± 1.64, at 20:30h=4.45 ± 1.13; and at 22:00 h= 4.36 ± 1.29. When bright light exposure was presented at 19:00h, the mean values of sleepiness were: at 19:00h= 4.73 ±1.27, at 20:30h= 5.08±1.24) and at 22:00h=5.43 ±1.62). No significant differences on sleepiness were observed after bright light exposure at 19:00h. Conclusions: The study showed an effect on sleepiness when light exposure was presented at 21:00h. This result might suggest that bright light exposure close to sunset would not produce a perceived reduction of sleepiness. Support: CNPq (501766/2007-3; 500782/2008-3; 472153/2006-4; 307919/2006-4); CAPES, FAPESP (07/04648- 4; 06/59053-2), PIBIC-CNPq, Ambulatory Monitoring Inc. Publication History Article published online: 16 June 2026 © 2009. Brazilian Sleep Academy. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Revinter Publicações Ltda. Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil