The Impact of Blue and Red Lights on Objective and Subjective Alertness in the Afternoon

Light affects non-visual pathways in ways not fully understood. The suppression of melatonin by light at night has been postulated as the mediating factor for improved nocturnal performance and alertness. However, recent work by the researchers’ laboratory shows that long-wavelength (red) light, which does not suppress melatonin, positively impacts alertness and performance at night and in the early morning. Here the researchers report the effects of narrowband red and blue light exposures on alertness, as measured by EEG, and on subjective sleepiness, as measured by the Karolisnka Sleepiness Scale (KSS) during the middle of the afternoon when melatonin levels are very low. Subjects reported less sleepiness using the KSS scale after red light (RL) and blue light (BL) than after dark (D), but the differences were not statistically significant. Consistently then, light can impact alertness without affecting melatonin.