Broad Spectrum Light for Seasonal Affective Disorder

Sufferers of Seasonal Affective Disorder (SAD) experience the winter blues more strongly than most people. Their depression deepens; they crave carbohydrates and sweets; they feel the need to sleep more hours than normal. They may consider themselves to be incompetent in some way. Many of these symptoms have been linked to light deprivation and abnormal circadian, or daily, rhythms. Light therapy, using broad-spectrum lighting, can help to alleviate winter SAD depression. Have a question? Get an answer from a doctor now!

Broad-Spectrum Light

Broad-spectrum light, unlike full-spectrum light, does not emit ultraviolet rays that are harmful to the eyes and skin. It is intended to produce a bright, white light that is safe for the SAD user. Sunlight has a Color Rendering Index (CRI) of 100; broad-spectrum lighting has a CRI between 80 to 82.

Duration of Therapy

Broad-spectrum light therapy, whether from a light box or a light-emitting visor, should take place once a day, for at least 30 minutes, but for no more than 3 hours. Usually, SAD sufferers begin to feel better after only 1 week of therapy.

Why Light Therapy Works

During the fall and winter months, when light levels are lower, low-light messages sent via the eyes to the brain register in the pineal gland. This gland is responsible for secreting the hormone melatonin, which controls how much sleep a human body needs. Less light means more sleep, and that, in some cases, can lead to an urge to sleep too much, adding to depression.


Broad-spectrum light needs to be close enough, but not too close to the person with SAD, to avoid damage to the eyes. A distance of 20 to 28 inches is recommended for a broad-spectrum light box with an output of 10,000 lux (a unit of illumination).


SAD, otherwise known as” the winter blues,” was discovered by the National Institute of Health in 1982. In 1984, researchers and scientists found that light therapy was beneficial to combat depression associated with the disorder.

By: Mary Osborne