DIURNAL SPECTRAL SENSITIVITY OF THE ACUTE ALERTING EFFECTS OF LIGHT
Diurnal Spectral Sensitivity of the Acute Alerting Effects of Light
Shadab A. Rahman, PhD1,2; Erin E. Flynn-Evans, PhD1,2; Daniel Aeschbach, PhD1,2,3; George C. Brainard, PhD4; Charles A. Czeisler, MD, PhD1,2; Steven W. Lockley, PhD1,2
1Division of Sleep Medicine, Department of Medicine, Brigham and Women's Hospital, Boston, MA; 2Division of Sleep Medicine, Department of Medicine, Harvard Medical School, Boston, MA; 3Institute of Aerospace Medicine, German Aerospace Center, Cologne, Germany; 4Department of Neurology, Thomas Jefferson University, Philadelphia, PA
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 × 1013 photons/cm2/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.
Measurements and Results:
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.
Rahman SA; Flynn-Evans EE; Aeschbach D; Brainard GC; Czeisler CA; Lockley SW. Diurnal spectral sensitivity of the acute alerting effects of light. SLEEP 2014;37(2):271-281.