Abstract
Exposure to bright light is typically intermittent in our daily life. However, the acute effects of intermittent light on alertness and sleep have seldom been explored. To investigate this issue, we employed within-subject design and compared the effects of three light conditions: intermittent bright light (30-min pulse of blue-enriched bright light (~1000 lux, ~6000 K) alternating with 30-min dim normal light (~5 lux, ~3600 K) three times); continuous bright light; and continuous dim light on subjective and objective alertness and subsequent sleep structure. Each light exposure was conducted during the three hours before bedtime. Fifteen healthy volunteers (20 ± 3.4 years; seven males) were scheduled to stay in the sleep laboratory for four separated nights (one for adaptation and the others for the light exposures) with a period of at least one week between nights. The results showed that when compared with dim light, both intermittent light and continuous bright light significantly increased subjective alertness and decreased sleep efficiency (SE) and total sleep time (TST). Intermittent light significantly increased objective alertness than dim light did during the second half of the light-exposure period. Our results suggested that intermittent light was as effective as continuous bright light in their acute effects in enhancing subjective and objective alertness and in negatively impacting subsequent sleep.
Highlights
Light has image-forming visual effects via rods and cones, and non-image-forming (NIF) visual effects through melanopsin-expressing intrinsically photosensitive retinal ganglion cells [1]
We aimed to explore the acute effects of intermittent light exposure during evening on alertness and the subsequent nocturnal sleep parameters (including sleep onset latency (SOL), sleep efficiency (SE), total sleep time (TST), wakefulness after sleep onset (WASO), Non-rapid eye movement (REM) sleep stages (N1, N2, and N3), and REM
As for the objective alertness across time, our data indicated that the subjects in the intermittent light condition performed significantly better in the Psychomotor Vigilance Task (PVT) in the assessments following the switching between dim light and bright light during the second half light exposure period than that in dim light, even in continuous light conditions
Summary
Light has image-forming visual effects via rods and cones, and non-image-forming (NIF) visual effects through melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs) [1]. Public Health 2018, 15, 524; doi:10.3390/ijerph15030524 www.mdpi.com/journal/ijerph
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