Comparative Effects of Red and Blue LED Light on Melatonin Levels During Three-Hour Exposure in Healthy Adults

Circadian rhythms, essential for regulating human physiology and behavior, are influenced by light exposure, particularly at night. This study examined the impact of red (631 nm) and blue (464 nm) LED light on melatonin secretion, a key circadian marker. Twelve participants aged 19-55 years were exposed to red and blue light for three hours (9:00 p.m.-midnight), with hourly saliva samples analyzed via ELISA to track melatonin levels. Initially, melatonin levels were comparable under both light conditions. After one hour, both lights suppressed melatonin, but differences emerged after two hours: blue light-maintained suppression, with levels at 7.5 pg/mL, while red light allowed recovery to 26.0 pg/mL (p = 0.019). This pattern persisted at the third hour. Blue light had stronger suppression effects, particularly in younger participants and men. These results underscore blue light's disruptive effects on circadian health and highlight red light as a less disruptive alternative for nighttime environments.