Awakening effects of blue-enriched morning light exposure on university students' physiological and subjective responses

Abstract

We investigated physiological and subjective responses to morning light exposure of commercially available LED lighting with different correlated colour temperatures to predict how LED-based smart lighting employed in future learning environments will impact students. The classical markers of the circadian system (melatonin and cortisol), as well as the subjective perception of sleepiness, mood, and visual comfort, were compared. Fifteen university students underwent an hour of morning light exposure to both warm (3,500 K) and blue-enriched (6,500 K) white lights at recommended illuminance levels for classrooms and lecture halls (500 lux). The decline of melatonin levels was significantly greater after the exposure to blue-enriched white light. Exposure to blue-enriched white light significantly improved subjective perception of alertness, mood, and visual comfort. With regard to cortisol, we did not find a significant difference in the cortisol decrement between the two light conditions. Our findings suggest that the sensitivity of physiological and subjective responses to white LED light is blue-shifted. These findings, extending the already known effects of short-wavelength light on human physiology, reveal interesting practical implications. Blue-enriched LED light seems to be a simple yet effective potential countermeasure for morning drowsiness and dozing off in class, particularly in schools with insufficient daylight.

Figure 1

Changes in (a) salivary melatonin (n = 11) and (b) cortisol levels (n = 15) before and after the light exposure. The data for WL and BL conditions are plotted with circles and triangles, respectively. An asterisk indicates significance at p < 0.05. The means ± s.e.m. of experimental results are shown.

Figure 2

The spectral power distribution (solid line) with melanopic weighted power (dashed line) for the two light conditions: (a) warm white light and (b) blue-enriched white light.