Evening exposure to a light-emitting diodes (LED)-backlit computer screen affects circadian physiology and cognitive performance

Mar 19, 2011Journal of applied physiology (Bethesda, Md. : 1985)

Evening use of LED computer screens affects body clock and thinking skills

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Abstract

A 5-hour evening exposure to a white LED-backlit screen with more than twice the light emission at 464 nm significantly suppressed melatonin levels in young males.

The LED screen exposure resulted in a significant decrease in the evening rise of endogenous melatonin.
Subjective and objective measures of sleepiness were reduced, indicated by fewer slow eye movements and lower EEG low-frequency activity.
Cognitive performance was enhanced in several areas, including sustained attention and working memory, when using the LED screen compared to the non-LED screen.
Both screen types were rated similarly for quality and visual comfort, although the non-LED screen was perceived as brighter.
The findings suggest that the light spectrum from screens may influence circadian rhythms, alertness, and cognitive abilities.

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Many people spend an increasing amount of time in front of computer screens equipped with light-emitting diodes (LED) with a short wavelength (blue range). Thus we investigated the repercussions on melatonin (a marker of the circadian clock), alertness, and cognitive performance levels in 13 young male volunteers under controlled laboratory conditions in a balanced crossover design. A 5-h evening exposure to a white LED-backlit screen with more than twice as much 464 nm light emission {irradiance of 0,241 Watt/(steradian × m(2)) [W/(sr × m(2))], 2.1 × 10(13) photons/(cm(2) × s), in the wavelength range of 454 and 474 nm} than a white non-LED-backlit screen [irradiance of 0,099 W/(sr × m(2)), 0.7 × 10(13) photons/(cm(2) × s), in the wavelength range of 454 and 474 nm] elicited a significant suppression of the evening rise in endogenous melatonin and subjective as well as objective sleepiness, as indexed by a reduced incidence of slow eye movements and EEG low-frequency activity (1-7 Hz) in frontal brain regions. Concomitantly, sustained attention, as determined by the GO/NOGO task; working memory/attention, as assessed by "explicit timing"; and declarative memory performance in a word-learning paradigm were significantly enhanced in the LED-backlit screen compared with the non-LED condition. Screen quality and visual comfort were rated the same in both screen conditions, whereas the non-LED screen tended to be considered brighter. Our data indicate that the spectral profile of light emitted by computer screens impacts on circadian physiology, alertness, and cognitive performance levels. The challenge will be to design a computer screen with a spectral profile that can be individually programmed to add timed, essential light information to the circadian system in humans.

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Evening exposure to a light-emitting diodes (LED)-backlit computer screen affects circadian physiology and cognitive performance

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