Temporal Dynamics of Subjective and Objective Alertness During Exposure to Bright Light in the Afternoon for 5 h

Abstract

Light can induce an alertness response in humans. The effects of exposure to bright light vs. dim light on the levels of alertness during the day, especially in the afternoon, as reported in the literature, are inconsistent. This study employed a multiple measurement strategy to explore the temporal variations in the effects of exposure to bright light vs. regular office light (1,200 lx vs. 200 lx at eye level, 6,500 K) on the alertness of participants for 5 h in the afternoon. In this study, 20 healthy adults (11 female; mean age 23.25 ± 2.3 years) underwent the Karolinska sleepiness scale (KSS), the auditory psychomotor vigilance test (PVT), and the waking electroencephalogram (EEG) test for two levels of light intervention. The results yielded a relatively lower relative delta power and a relatively higher beta power for the 1,200 lx condition in comparison with the 200 lx condition. However, the light conditions elicited no statistically significant differences in the KSS scores and performance with respect to the PVT. The results suggested that exposure to bright light for 5 h in the afternoon could enhance physiological arousal while exerting insignificant effects on subjective feelings and performance abilities relating to the alertness of the participants.

Alerting Effect of Light: A Review of Daytime Studies

“…Another study reported that the increase in illuminance from 200 lx to 1200 lx for five hours starting at 14:00 elevated physiological markers of alertness. However, it did not enhance either subjective or performative indicators of alertness [50]. Nevertheless, if the physiological markers of alertness do not translate to either subjective or performative indicators then such a scenario would be ineffective for non-visual stimulation in an office setting.…”

“…Luo et al [50] compared the alerting effect of regular office light (1200 lx vs. 200 lx) for 5 hours in the afternoon and found that in comparison to subjective and performative indicators, the EEG activity may be more responsive to the bright light-induced alertness response during the day.…”