Effect of Light Exposure Before Bedtime on Polysomnography and Sleep Quality: A Randomized Crossover Study

This study examined the effects of bedroom lighting with pre-bedtime activities two hours before bedtime on sleepiness and polysomnography (PSG) sleep in community-dwelling adults with poor sleep.

A balanced crossover design was used with 24 healthy adults. Four lighting conditions under two activity situations (unrestricted (A1) and restricted (A2) electronic device use two hours before bedtime) were tested using adjustable LED lights: (E2: 3000K, 160 lux; E3: 5000K → 3000K, 160 → 30 lux; E4: 5000K, 160 lux) and compared to standard fluorescent lighting (E1: 5000K, 160 lux). The protocol lasted 8 nights (4 lightings × 2 activity conditions), with the whole night PSGmeasure, subjective sleep perception at wake-up, and sleepiness (Stanford Sleepiness Scale) measured hourly 2 hr before bedtime.

Results showed that sleep latency was 10.62 min longer when exposed to 5000k LED light than to 5000k FL. Exposure to other lower color temperature lights did not have a significant difference in sleepiness and PSGsleep. However, participants felt drowsier and had a shorter PSG sleep latency of 6.08 min when the use of electronic devices was not allowed.

A 5000k LED light leads to longer sleep latency compared to a 5000k fluorescent light. Restriction of electronic device use before bedtime improves sleep onset in healthy adults. Managing ambient light exposure with lower color temperature LED light and reducing electronic device use 2 hr before bedtime may improve sleep quality in healthy adults.