Do the lights really work?

Researchers at more than 15 medical centers and clinics in both the U.S. and abroad have had much success with light therapy in patients with clear histories of SAD for at least several years. Marked improvement is usually observed within a week, if not sooner, and symptoms usually return in about the same amount of time when the lights are withdrawn. Most users, therefore, maintain a consistent daily schedule beginning, as needed, in fall or winter and usually continuing until the end of April, by which time outdoor light is sufficient to maintain good mood and high energy. Some people can skip treatments for one to three days, occasionally longer, without ill effect, but most start to slump quickly when treatment is interrupted.

How do the lights work?

The therapeutic level of illumination has several known physiological effects, though its therapeutic mechanism is still unclear. Blood levels of the light-sensitive hormone melatonin, which may be abnormally high at certain times of day, are rapidly reduced by light exposure. Depending on when bright light is presented, the body’s internal clock–which controls daily rhythms of body temperature, hormone secretion, and sleep patterns–shifts ahead or is delayed when stimulated by light. These physiological time shifts may be the basis of the therapeutic response. Light may also amplify the day-night difference in these rhythms. Research into the possible mechanisms is currently underway, and the final answer is not yet in.