The effects of spectral tuning of evening ambient light on melatonin suppression, alertness and sleep

📖 Top 30% JournalMay 5, 2017Physiology & behavior

How different colors of evening light affect melatonin, alertness, and sleep

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Abstract

Control-adjusted melatonin suppression was significantly reduced with blue-depleted LED light compared to standard fluorescent light.

Sixteen healthy participants were exposed to two different light sources for 8 hours prior to bedtime in a controlled setting.
Subjective sleepiness did not differ between the blue-depleted LED light and standard fluorescent light conditions.
Auditory reaction times were significantly slower under blue-depleted LED light compared to fluorescent light 30 minutes before bedtime.
EEG measurements indicated reduced alertness under blue-depleted LED light, demonstrated by increased spectral power in the delta-theta frequency range.
No significant differences were found in total sleep time, sleep efficiency, or slow-wave activity between the two light conditions.
An order effect on sleep variables was noted, with participants receiving blue-depleted LED light first showing increased total sleep time, sleep efficiency, and slow-wave activity.

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We compared the effects of bedroom-intensity light from a standard fluorescent and a blue- (i.e., short-wavelength) depleted LED source on melatonin suppression, alertness, and sleep. Sixteen healthy participants (8 females) completed a 4-day inpatient study. Participants were exposed to blue-depleted circadian-sensitive (C-LED) light and a standard fluorescent light (FL, 4100K) of equal illuminance (50lx) for 8h prior to a fixed bedtime on two separate days in a within-subject, randomized, cross-over design. Each light exposure day was preceded by a dim light (<3lx) control at the same time 24h earlier. Compared to the FL condition, control-adjusted melatonin suppression was significantly reduced. Although subjective sleepiness was not different between the two light conditions, auditory reaction times were significantly slower under C-LED conditions compared to FL 30min prior to bedtime. EEG-based correlates of alertness corroborated the reduced alertness under C-LED conditions as shown by significantly increased EEG spectral power in the delta-theta (0.5-8.0Hz) bands under C-LED as compared to FL exposure. There was no significant difference in total sleep time (TST), sleep efficiency (SE%), and slow-wave activity (SWA) between the two conditions. Unlike melatonin suppression and alertness, a significant order effect was observed on all three sleep variables, however. Individuals who received C-LED first and then FL had increased TST, SE% and SWA averaged across both nights compared to individuals who received FL first and then C-LED. These data show that the spectral characteristics of light can be fine-tuned to attenuate non-visual responses to light in humans.

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