Scientists believe Seasonal Affective Disorder (SAD) is caused by the reduced light levels during the fall and winter. When the light levels change, it influences our circadian rythym. A 24-hour clock, the circadian rythym affects the way we eat, sleep, and behave primarily through two brain chemicals called melatonin and serotonin. While melatonin induces sleepliness, serotonin promotes feelings of well-being.

Since less light is believed to be a factor in SAD, initially, researchers applied thirty minutes of  full-spectrum light or white light in the morning to see whether it reduced the symptoms of depression. Although there is no set definition, full-spectrum light closely mimics natural sunlight and emits all visible wavelengths of light.

Since then, there has been several research studies testing the efficacy of different wavelengths. and some controversy has resulted.  When different research studies have been done, the following are some of the outcomes:

• When blue light and green light were compared to red light, researchers found blue and green light were more effective in treating SAD.
• When 8 to 10 lux of blue light was compared to 10,000 lux of white light, the blue light was found to be equally as effective in treating SAD as the white light and twice as effective in suppressing melatonin and resetting the circadian rythym.
• When 350 lux of green light was compared against 10,000 lux of white light, the green light was comparable in suppressing melatonin and adjusting sleep phase shifts.
• When sleepy men and women were bathed in six and a half hours to the same intensity of blue light and green light, those bathed in blue light were less sleepy, had quicker reaction times, and had less lapses of attention.

From these studies, it would appear that overall blue light is more effective than either white or green light, but there has been some concern that blue light can increase the risk of macular degeneration in those susceptible to it. However, healthy retinas have chemical defenses to protect against blue light damage. Consequenty, unless you have diabetes, a pre-existing eye disease, or health problems, blue light should not be an issue. However, regardless of what color light therapy device you decide to buy, I would recommend consulting your physician or opthamologist first.