Abstract
The characteristics of light - intensity, spectrum, distribution, duration and timing - that support optimal vision are different from those that influence the circadian system. Since an increasing amount of land, air and sea transportation is conducted at night, the role of light in regulating circadian rhythms for operators will increase in importance in the near future. This paper reviews the state of the art regarding light and the human circadian system, and discusses potential implications and applications for such research information. Particular emphasis is placed on the application of light for helping to maintain alertness in individuals.