A study of nine young men suggests that blue light beats back sleepiness and dampens key physiological changes that normally occur in the late evening. Green-yellow light doesn't have the same effect. Blue light, or white light containing it, therefore, might help evening workers stay alert, the researchers say.
Certain light receptors in the eye affect how the body calibrates its internal clock and orchestrates daily oscillations in body temperature and heart rate. To better understand the role of light's color, or wavelength, in those processes, Christian Cajochen of the Psychiatric University Clinic in Basel, Switzerland, and his colleagues had male volunteers spend an evening and night in a room in which the researchers could control the color of the light.
Each subject participated in three rounds of the experiment, which had the same sequence of light and darkness except for one 2-hour period ending 1.5 hours before bedtime. In separate rounds, that period feature