The effects of LED lighting on sleep and sleepiness

Objectives: Several previous investigations indicate that blue light exposure during the night reduces melatonin secretion, improves vigilance and diminishes sleepiness. Moreover it has been demonstrated that a blue light dose administered in the evening can have a positive effect for shift workers. In the present study the effect of cool LED lighting exposure during daily hours has been investigated in two experiments: self-reported sleep and sleepiness have been assessed prior and post light exposure using a sleep diary and Karolinska Sleepiness Scale (KSS). Methods: In the first investigation (E1) the experimental light condition consisted in a 4000 K LED light and the control condition was the halogen lighting (2800 K); while in the experiment 2 (E2) a 6800 K LED lighting has been compared with a warm 3000 K LED light condition. In both experimental studies the cool light exposure duration was about 1 h and 40 subjects (20 females) were involved. Results: Data from E1 indicated that the experimental light condition had a positive effect on sleep latency who significantly decreased (P = 0.004). In the same vein, data from E2 showed shorter nightime awakenings (P = 0.04) and longer sleep time (P = 0.05) in participants exposed to cool LED lighting. No significant effects were observed on sleepiness self evaluations. Conclusions: The present results go in the direction of a better sleep quality and quantity, indicating a greater stability and continuity of sleep after the exposure to colder light. They also support previous results observed under different lighting conditions.