Rapid communication Blue light improves cognitive performance

Brainard et al. (2001) and Thapan et al. (2001) reported a non-visual photoreceptor system in humans, that is closely interlinked with circadian rhythms. It works independently of the scotopic and photopic photoreceptor systems and is intact in some individuals with amaurosis as well as with red–green color blindness (Lockley et al., 2006). The circadian photoreceptor system responds most sensitively to blue light with a wave length at approximately 460 nm (Berson et al., 2002; Brainard and Hanifin, 2005). Blue light needs much less energy to influence circadian rhythms than light waves in the scotopic or photopic spectrum (Lockley et al., 2003). These findings have successfully been used in clinical practice to improve sleep-wake disturbances in old patients with and without Alzheimer’s disease (Figueiro and Rea, 2005; Figueiro et al., 2003). Changes in the circadian rhythms due to different light have been expected to occur after hours or even days. Changes in body temperature have been found to occur after a 2 hour delay (Cajochen et al., 2005). However, exposing oneself to a blue environment or looking at a blue picture leads to the subjective impression of an immediate change in one’s alertness. This experience led us to the hypothesis, that effects of blue light may occur even after seconds and should lead, compared to light with a lower frequency, to an increase in alertness. If this hypothesis is true, a change in mental fitness should occur also during seconds, according to the activation model of Yerkes and Dodson (1908). If so, probands in a relaxed mood should experience an increase in cognitive efficiency when exposed to blue light, while subjects with an already elevated activation may suffer from increased emotional tension. We report a longitudinal pilot study evaluating this hypothesis.