Diurnal spectral sensitivity of the acute alerting effects of light

• Published in: Sleep (New York, N.Y.) Vol. 37; no. 2; pp. 271 - 281
• Main Authors: Rahman, Shadab A, Flynn-Evans, Erin E, Aeschbach, Daniel, Brainard, George C, Czeisler, Charles A, Lockley, Steven W
• Format: Journal Article
• Language: English
• Published: United States Associated Professional Sleep Societies, LLC 01-02-2014
• Subjects: Adult; Attention - physiology; Attention - radiation effects; Circadian Rhythm - physiology; Circadian Rhythm - radiation effects; Darkness; Diurnal Spectral Sensitivity of the Acute Alerting Effects of Light; Electroencephalography; Homeostasis; Humans; Light; Male; Sleep Stages - physiology; Sleep Stages - radiation effects; Time Factors; Wakefulness - physiology; Wakefulness - radiation effects; Young Adult; Alertness; sleep; circaidian; homeostatic; light; short-wavelength light
• ISSN: 0161-8105; 1550-9109
• DOI: 10.5665/sleep.3396

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.