Seasonal depression, also known as Seasonal Affective Disorder (SAD), is a medical condition characterized by symptoms of depression. As the name implies, symptoms begin to emerge during seasonal changes, most commonly in winter. Research indicates that SAD appears to be associated with light, most notably the lack of it. Full spectrum lights may serve as a substitute for missing sunlight, helping to relieve the symptoms of depression.
Although SAD is most common in winter, seasonal depression can also occur in summer, in which case, it is known as Reverse Seasonal Affective Disorder. Neither condition should be dismissed as mere cabin fever in winter, or feeling lazy and hazy in summer. In fact, SAD is a genuine mood disorder that, in severe cases, may increase the risk of suicide and require hospitalization.
Studies have shown that there is a higher incidence of SAD in areas where there tends to be more cloud cover than sunshine. Latitude also seems to affect the rate of occurrence. This has lead researchers and clinicians to theorize that regulated exposure to full spectrum lights may serve as a substitute for natural sunlight and improve symptoms of SAD. While this form of therapy was considered highly experimental not very long ago, many schools, employers, and public facilities now use these lights to ward off the winter blues.
Full spectrum lights seem to provide several benefits. For one thing, mood appears to be affected by how well people can see — perhaps even by the mechanical processes occurring in the eyes. In daylight, the cones of the eyes are activated, as opposed to forcing the ocular rods to compensate for night vision. Lights that include the full spectrum provide the closest simulation to natural sunlight by emulating the wavelengths of the sun’s zenith, the point when it is directly overhead in the sky at noon. There is no risk of exposure to ultraviolet light, however, which can harm skin and eyes.
Light also plays a role in regulating circadian rhythms, the human body’s internal alarm clock that signals when it’s the appropriate time to rise in the morning and retire to bed in the evening. This is evidenced by the fact that people who work “graveyard shifts” tend to experience SAD more frequently, since they often leave for work and come home in the dark. This scenario is likely to confuse the brain from properly distinguishing between night and day, resulting in a decrease in melatonin production. Full spectrum lights can help to minimize this effect by stimulating an increased release of this “feel good” hormone.
People should be aware that therapy with full spectrum lights is not the same as sitting under ordinary bright light bulbs purchased from a hardware store. Full spectrum refers to white light with a luminance of 2,500 to 10,000 lux, with the first number closely representing daybreak and the second full daylight. As a treatment, exposure to such lights is typically done while sitting in a light box for 30 to 60 minute intervals.