Diurnal Spectral Sensitivity of the Acute Alerting Effects of Light

• DOI: 10.5665/sleep.3396
• Publication Date: 2014-01-31T20:22:05Z
• Authors: Shadab A. Rahman; Erin E. Flynn-Evans; Daniel Aeschbach; George C. Brainard; Charles A. Czeisler; Steven W. Lockley
• Keywords: Adult; Male; Time Factors; Light; circaidian; homeostatic; Electroencephalography; 535; Darkness; Alertness; Circadian Rhythm; short-wavelength light; Young Adult; 03 medical and health sciences; 0302 clinical medicine; Homeostasis; Humans; Attention; Sleep Stages; sleep; Wakefulness; light

Previous studies have demonstrated short-wavelength sensitivity for the acute alerting response to nocturnal light exposure. We assessed daytime spectral sensitivity in alertness, performance, and waking electroencephalogram (EEG).Between-subjects (n = 8 per group).Inpatient intensive physiologic monitoring unit.Sixteen healthy young adults (mean age ± standard deviation = 23.8 ± 2.7 y).Equal photon density exposure (2.8 × 10(13) photons/cm(2)/s) to monochromatic 460 nm (blue) or 555 nm (green) light for 6.5 h centered in the middle of the 16-h episode of wakefulness during the biological day. Results were compared retrospectively to 16 individuals who were administered the same light exposure during the night.Daytime and nighttime 460-nm light exposure significantly improved auditory reaction time (P < 0.01 and P < 0.05, respectively) and reduced attentional lapses (P < 0.05), and improved EEG correlates of alertness compared to 555-nm exposure. Whereas subjective sleepiness ratings did not differ between the two spectral conditions during the daytime (P > 0.05), 460-nm light exposure at night significantly reduced subjective sleepiness compared to 555-nm light exposure at night (P < 0.05). Moreover, nighttime 460-nm exposure improved alertness to near-daytime levels.The alerting effects of short-wavelength 460-nm light are mediated by counteracting both the circadian drive for sleepiness and homeostatic sleep pressure at night, but only via reducing the effects of homeostatic sleep pressure during the day.