Scientists Shed New Light On The Body" s Rhythms Have you ever suffered from jet-lag, the fatigue and depression that comes from long hours spent in a jet aircraft traveling across the world over many time zones? Or like many people in northern European countries, have you ever suffered the dark depression of winter blues, the feelings of gloom that comes from facing the somber December and January winter days under dark, cloudy skies? Maybe all you need is a little light—and merely on a small patch of your skin. In fact, in experiments investigating the effect of light in raising our spirits, American scientists have done all their research using light played on the back of the subjects" knees. What could be a key to jet-lag and winter blues is the hormone melatonin, which is known to regulate body rhythms. It is secreted as night falls and it can be used to help to overcome jet-lag and some sleep disorders. The low level of melatonin we experience in winter when light is dull and daylight hours are shorter is said to be cause of that common feeling many people get in dull weather—winter depression. For years experts have experimented with treating jet-lag and seasonal affective disorder ( " winter depression" ) with light. They counsel victims to sit in front of lights simulating the sun" s natural wavelengths to restore melatonin. In 1996, Diane Boivin and colleagues at Harvard Medical School found even dim reading lamps worked in this way. Exposure to light sets off a complex response inside the bodies of animals and humans. A university team in New York said they had found that shining light on the skin could reset the body" s internal clock. They chose the back of the knee because it was easy to reach and away from the eyes, which is where many scientists had believed circadian rhythm is determined.