Who needs bright light and when? Mapping the interactions of lighting environments and individual differences in circadian light sensitivity

Kurzfassung

Light is the primary circadian time cue, but there are large inter-individual differences in how sensitive the circadian system is to light. Currently, it is not well understood how individual differences in light sensitivity interact with real-world light environments to determine sleep and circadian timing. We used a validated computational model to simulate sleep and circadian timing (predicted dim light melatonin onset) under realistic assumptions about light and work schedules. Simulations were repeated varying light sensitivity (translated to equivalent ED50 values for interpretability), as well as evening, morning and daytime illuminances. Brighter evening light led to later predicted circadian and sleep timing, with this effect being amplified by high light sensitivity. Reducing evening light is particularly beneficial for those with high light sensitivity or a biological tendency towards delayed sleep timing. Brighter morning light was beneficial for individuals with a long circadian period, or those with both high light sensitivity and high evening light. However bright morning light could be maladaptive in individuals with a short circadian period, or those with low light sensitivity and low evening light. Brighter daylight attenuated the delaying effects of evening light across conditions, indicating that increasing daylight was the most universally beneficial lighting intervention. Our results demonstrate how circadian light sensitivity can be used to tailor individual-level solutions that support optimal sleep and circadian timing.