Effects of ambient illumination over days on human vigilance performance.

Detection rates of 36 college students were measured for three days in an auditory vigilance task under one of three conditions of ambient illumination: dark (less than .33 lx), low (86 lx), and high (170 lx) intensity levels. Within-session performance decrements were seen in all conditions. Increasing the intensity of ambient illumination improved vigilance performance, an effect which became more potent over days. These results are discussed in terms of arousal theory and habituation.