Home lighting before usual bedtime impacts circadian timing: a field study

Area of Science:

• Chronobiology
• Sleep Science
• Human Physiology

Background:

• Laboratory studies indicate evening light exposure can suppress melatonin production.
• The impact of typical household light intensity on circadian phase in a home environment is not well understood.

Purpose of the Study:

• To measure household light intensity levels during evening hours.
• To determine if varying home light exposure before bedtime can shift circadian phase.
• To assess the effect of light intensity on dim light melatonin onset (DLMO).

Main Methods:

• A 3-week study with eight healthy subjects in two counterbalanced conditions: dim light week (approx. 3 lux) and bright light week (approx. 65 lux).
• Subjects minimized or maximized home light exposure for 4 hours before habitual bedtime.
• Circadian phase was assessed using dim light melatonin onset (DLMO) and wrist actigraphy.

Main Results:

• Subjects significantly increased light intensity in the bright week (average 65 lux) compared to the dim week (average 3 lux).
• Maximizing home light exposure resulted in a later bedtime (14 min average) and a significantly later DLMO (1:03 h average).
• Every subject demonstrated a later DLMO after the bright light week compared to the dim light week.

Conclusions:

• Household light intensity in the hours before habitual bedtime can alter circadian timing.
• Reducing evening light exposure is recommended to prevent circadian misalignment.
• Home light management is a viable strategy for influencing internal body clock timing.