How does light exposure affect circadian rhythms and sleep cycles? This review article provides an analysis of many studies exploring the effects of different wavelengths and durations of light exposure on sleep. I was curious about blue vs. red-orange:
tandfonline.com/doi/abs/10.108…
tandfonline.com/doi/abs/10.108…
“Appleman et al. (2013) conducted a 12-day study where 21 subjects, randomly divided into two groups, received either short-wavelength (blue, peak 476 nm) light for 2h in the morning and light filtered (<535 nm) with orange-tinted glasses for 3h in the evening (advance group)…”
“…or at opposite times, that is orange-tinted glasses in the morning and blue light in the evening (delay group). Subjects kept their normal schedule for the first 5d and received morning and evening light exposures the following 7d in addition to a fixed sleep schedule…”
“…(advanced by 90 min from the baseline). The study showed that the direction of circadian phase change is determined by the light-dark exposure, not by the fixed sleep schedule, and that both morning and evening light exposures need to be controlled to shift circadian phase.”
“After 7 days on the fixed 90-min advanced sleep schedule, circadian phase advanced by 132 ± 19 min in advance group and delayed by 59 ± 7.5 min in delay group.”
Meaning blue light exposure in the morning and orange at night shifted sleep cycles more than 2 hours earlier, while subjects stayed up an hour later with these cycles in reverse.
Lighting is one of the most important factors for sleep and circadian rhythms. If you struggle with sleep hygiene, it is definitely recommended to avoid blue and colder white lights in the hours before sleep.
Anecdotally, I’ve found that orange-red lights help tremendously with falling asleep in the evening, and that a few hours of exposure to warmer colored lights improves sleep quality. Also, it is easier to work for long hours if the lights do not remain the same color.
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