In a recent NIMH study, a group of these depressives were treated with amounts of light that simulated that of summer days. Short winter days were stretched by six extra hours of light. The subjects were awakened before sunrise to bask in three hours of light, and dusk was delayed for three more. Since sunlight is thought to be the missing element, the subjects were flooded with an artificial light that most closely resembles the full broad spectrum of the sun. At 20 times the intensity of normal indoor lighting, the light approximated the sensation of sitting on a shady porch or under a tree in mid-summer.
Fluorescent lamps are roughly three times more intense than ordinary light bulbs.
A bank of eight 4-watt fluorescent bulbs at eye level lit the participants' rooms as they read, worked, or moved around. Within days this group responded with measurable mood changes, says Rosenthal. Their symptoms eased and energy levels rose, while a control group with a different threshold of light showed no change in behavior. It is true, though, that waking up these people and exposing them to this light treated their symptoms. Whether it is the break in sleep pattern, the wavelengths or intensity of light, or some other factor we can't say at this point.