Monochromatic light exposure: effects on daytime sleepiness

During diurnal Circadian phase, “Red” light (630 nm) administration is associated with greater alerting effects when compared to “Blue” light (470 nm). Conversely, short wavelength light has been found to affect Circadian output exerting non-visual responses in suppressing melatonin; thus reducing sleepiness and increasing performance of cognitive tasks during the night. Throughout exposure to different light spectra by means of a LED light box, we aimed to disentangle a role for sleep Homeostatic pressure to modulate alerting effects of monochromatic light administration during postprandial hours. Eleven participants (6 Males) were exposed alternatively to 45 minutes of both light Conditions (Blue/Red). Baseline (BL - 10.00 am), Pre-Light (L1 - 2.00 pm) and Post-Light (L2 - 3.00 pm). Objective sleepiness was assessed by Psychomotor Vigilance Task (PVT); in addition Visual Analogue Scale (VAS) was administered in order to assess subjective Vigilance. Two separate 2 9 3 mixed-model ANOVAs showed a significant time effect on both objective (F(2,40) = 8.2963; P= 0.00097) and subjective measures (F(2,40) = 6.410; P =0.00385) with participants showing increased sleepiness. A significant interaction effect was found only for PVT (F(2,40) = 3.4611 ; P = 0.04108); Post-hoc comparison found that daytime sleepiness was reduced only on Post-Light exposure in the Blue condition. Given these preliminary results, it is possible to hypothesize a wavelength sensibility also for homeostatic drive.