NEW YORK, NY. Plants and animals all have circadian rhythms which control many functions such as the opening and closing of flowers, sleep/wake cycles, body temperature and melatonin secretion. Research has shown that the internal clock governing circadian rhythms in humans can be reset by exposure to light at various points in the cycle. This light exposure is usually transmitted through the retina of the eye. Now researchers at Cornell University report that shining a strong light (13,000 lux) on the back of the knees has an effect similar to that obtained by shining the light at the eyes. The researches postulate that bilirubin and hemoglobin act as photoreceptors and somehow carry the "light message" to the pineal gland or interact with melatonin to reset the internal clock. Light therapy is useful in treating aberrant sleep patterns and alleviating winter depression (SAD). If light was directed at the back of the knees rather than into the eyes light therapy could presumably be performed during the night or early morning without actually waking the patient. However, more research is required to prove that aiming the light at the back of the knees has the same therapeutic effect as directing it right on to the retina.
Oren, Dan A. and Terman, Michael. Tweaking the human circadian clock with light. Science, Vol. 279, January 16, 1998, pp. 333-34
Campbell, Scott S. and Murphy, Patricia J. Extraocular circadian phototransduction in humans. Science, Vol. 279, January 16, 1998, pp. 396- 99