Effects of daytime exposure to short-wavelength-enriched white light on alertness and cognitive function among moderately sleep-restricted university students

We examined the impact of an 8-h exposure to short-wavelength-enriched white light during the day on the cognitive performance, alertness, and mood of moderately sleep-restricted university students in a simulated classroom setting. A total of 28 participants (mean age: 23.57 +/- 2.69; 19 female) were assigned to one of two short-wavelength-enriched white light conditions, each with an equal melanopic daylight efficacy ratio (melDER similar to 0.9). However, they differed in photopic and melanopic illuminances, falling within the upper and lower limits of prescribed standards for classroom lighting: low illuminance (LI; 309.33 +/- 3.04 horizontal photopic and 128.26 +/- 7.37 vertical melanopic EDI lux) and high illuminance (HI; 513 +/- 12.59 horizontal photopic and 213.70 +/- 11.62 vertical melanopic EDI lux). Cognitive performance, procedural memory, declarative memory, subjective alertness, and mood were evaluated using the N-back Task, Finger Tapping Task, Free Recall Task, Modified Karolinska Sleepiness Scale, and Visual Analogue Scales, respectively. No statistically significant differences were observed in any of the memory, alertness, and mood measures between the two lighting conditions (p.adjusted > 0.05). These results indicate that short-wavelength-enriched light exposures at illuminances falling within the upper and lower limits of current classroom lighting standards do not adversely affect cognitive performance, alertness, and mood, as assessed in this study. These findings have meaningful implications for classroom lighting design, providing an opportunity to enhance energy efficiency without compromising working memory, procedural memory, declarative memory, subjective alertness, and mood.