Daily Profiles of Light Exposure and Evening Use of Light-emitting Devices in Young Adults Complaining of a Delayed Sleep Schedule

Feb 22, 2018Journal of biological rhythms

Daily Light Exposure and Evening Use of Screens in Young Adults with Late Sleep Patterns

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Abstract

Participants with a delayed sleep schedule had a smaller light-dark cycle amplitude compared to controls, which is associated with a later dim light melatonin onset (DLMO).

Smaller amplitude of the light-dark cycle was due to decreased daytime exposure and increased nighttime exposure.
Total exposure to blue light was lower in participants with delayed sleep schedules, possibly due to reduced outdoor light exposure.
Lower daily exposure to blue light correlated with a later DLMO.
Delayed participants experienced higher light exposure 2 hours after DLMO, a time associated with phase delays.
Increased light exposure occurred 8 to 10 hours after DLMO, mainly during sleep, which may affect circadian timing.
Self-reported use of light-emitting devices before bedtime was higher in delayed participants and linked to a later DLMO.

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A number of factors can contribute to a delayed sleep schedule. An important factor could be a daily profile of light exposure favoring a later circadian phase. This study aimed to compare light exposure between 14 young adults complaining of a delayed sleep schedule and 14 matched controls and to identify possible associations between habitual light exposure and circadian phase. Exposure to white and blue light was recorded with ambulatory monitors for 7 consecutive days. Participants also noted their daily use of light-emitting devices before bedtime. Endogenous circadian phase was estimated with the dim light melatonin onset (DLMO) in the laboratory. The amplitude of the light-dark cycle to which the subjects were exposed was smaller in delayed than in control subjects, and smaller amplitude was associated with a later DLMO. Smaller amplitude was due to both decreased exposure in the daytime and increased exposure at night. Total exposure to blue light, but not to white light, was lower in delayed subjects, possibly due to lower exposure to blue-rich outdoor light. Lower daily exposure to blue light was associated with a later DLMO. Timing of relative increases and decreases of light exposure in relation to endogenous circadian phase was also compared between the 2 groups. In delayed subjects, there was a relatively higher exposure to white and blue light 2 h after DLMO, a circadian time with maximal phase-delaying effect. Delayed participants also had higher exposure to light 8 to 10 h after DLMO, which occurred mostly during their sleep episode but may have some phase-advancing effects. Self-reported use of light-emitting devices before bedtime was higher in delayed than in control subjects and was associated with a later DLMO. This study suggests that individuals complaining of a delayed sleep schedule engage in light-related behaviors favoring a later circadian phase and a later bedtime.

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Daily Profiles of Light Exposure and Evening Use of Light-emitting Devices in Young Adults Complaining of a Delayed Sleep Schedule

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