Lighting research & technology (London, England : 2001)Jun 14, 2019

How length of exposure and light color affect nighttime melatonin levels in teens and adults

Circadian Biology Weekly Brief ↗PubMed ↗DOI ↗

Updated Mar 28, 2026

Abstract

Longer exposure to light significantly suppresses melatonin levels, with adolescents showing a 43% suppression after exposure to blue light compared to 29% for warm light.

Melatonin suppression is greater with longer light exposure durations.
Different light spectra have varying effects on melatonin levels, with cool light (5600 K) being more effective than warm light (2700 K).
Adolescents demonstrate greater sensitivity to blue light compared to adults.
After exposure to cool light, adolescents show a significant increase in melatonin suppression compared to adults.

Simplified

This study investigated how light exposure duration affects melatonin suppression, a well-established marker of circadian phase, and whether adolescents (13-18 years) are more sensitive to short-wavelength (blue) light than adults (32-51 years). Twenty-four participants (12 adolescents, 12 adults) were exposed to three lighting conditions during successive 4-h study nights that were separated by at least one week. In addition to a dim light (<5 lux) control, participants were exposed to two light spectra (warm (2700 K) and cool (5600 K)) delivering a circadian stimulus of 0.25 at eye level. Repeated measures analysis of variance revealed a significant main effect of exposure duration, indicating that a longer duration exposure suppressed melatonin to a greater degree. The analysis further revealed a significant main effect of spectrum and a significant interaction between spectrum and participant age. For the adolescents, but not the adults, melatonin suppression was significantly greater after exposure to the 5600 K intervention (43%) compared to the 2700 K intervention (29%), suggesting an increased sensitivity to short-wavelength radiation. These results will be used to extend the model of human circadian phototransduction to incorporate factors such as exposure duration and participant age to better predict effective circadian stimulus.

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How length of exposure and light color affect nighttime melatonin levels in teens and adults

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