The Lighting Research Center (LRC) is    part of Rensselaer Polytechnic Institute    of Troy, N.Y., and is the leading    university-based research center    devoted to lighting. The LRC offers the    world's premier graduate education in    lighting, including one- and two-year    master's programs and a Ph.D.    program. Since 1988 the LRC has built    an international reputation as a reliable    source for objective information about    lighting technologies, applications, and    products. The LRC also provides    training programs for government    agencies, utilities, contractors, lighting    designers, and other lighting    professionals. Visit

The Light and Health program at the LRC bridges the gap between science and applications by striving to better understand how the visual and circadian systems work, the lighting characteristics that affect them, and ways to develop the means of applying and measuring light that is effective to both visual and circadian systems.

Biological rhythms that repeat at approximately every 24 hours are called circadian rhythms. Light is the main stimulus that helps the circadian clock, and thus circadian rhythms, keep a synchronized rhythm with the solar day. If we are not exposed to sufficient amount of light of the right spectrum, for a sufficient amount of time, and at the right timing, our biological clocks become desynchronized with the solar day; decrements in physiological functions, neurobehavioral performance and sleep may occur.

Lighting characteristics that are effective to the circadian system are different than the ones effective to the visual system. A better understanding of the quantity, spectrum, timing, duration, and distribution of light that is effective for the circadian system is essential, so that light can be applied to mitigate the symptoms of Alzheimer抯 disease, seasonal affective disorder, sleep deprivation, and jet lag.