Seasonal Affective Disorder (SAD) may be identified by a number of symptoms, including depression, sadness, anxiety, irritability and violence, decreased physical activity, increased appetite and hypersomnia – sleeping for very long hours.

Symptoms of SAD typically surface in the winter months and were initially linked to the onset of the holidays and feelings of aloneness many people experience at that time of year. Since, then, scientists have identified predictable human patterns that directly correlate to the number of daylight hours in a given day.

“As daylight began noticeably decreasing in September,” writes Dr. Lindsley, “some people were affected. By the time the days bracketing the winter solstice came, almost everyone in the study group was affected. Then, as the season moved away from the solstice toward spring with lengthening daylight hours, the number of affected people began to decline. By the end of May, almost everyone was back to their old selves, some unfortunately even switching into what psychiatrists call mania.”

To support their theory of SAD symptoms being linked to hours of daylight, scientists supplied light to see if it would reverse the effects of SAD. While dimmer, yellow light produced no effect, bright lights with a frequency spectrum simulating that of sunlight did reverse the effects of SAD for most patients. Further studies support the theory that decreased daylight produces SAD in affected individuals and that the right kind of lighting therapy can result in marked improvement in most people.

From “Seasonal Affective Disorder (SAD): About Light, Depression and Melatonin,” by Gila Lindsley, Ph.D., A.C.P.