"Sighted people utilize the light-dark cycle to synchronize their circadian rhythms to the 24 hour day. This is a generally accepted fact today. Yet for many years the light -dark cycle was discounted as a time giver in favor of social cues. It was thought that humans had evolved past other primates to be relatively unaffected by light."

"Ordinary room light, which was used in these studies, was not sufficiently intense to be effective in humans. It seems that humans require brighter light than other animals... [it should be mentioned that some people are more sensitive to light than others]."

"The second implication was that we could substitute bright artificial light for sunlight to experimentally, or perhaps therapeutically, manipulate biological rhythms in humans. This was first tested in a patient that came to us with a complaint of a seasonal mood disorder. He became depressed as the days grew shorter and came out of his depression as the days lengthened. We exposed him to 2000 lux light in the morning and in the afternoon, that is before dawn and after dusk, to effectively lengthen his winter days to those that would be similar to a spring photoperiod when he would spontaneously switch out of his depression. After ten days of light treatment, his depression remitted."

"Evidence from studies on normal individuals as well as the general population confirms that the types of behavioral changes seen in patients with SAD during the winter, such as low energy level, overeating, weight gain, and increased sleep length, are also found in a certain percentage of the normal subjects, albeit to a lesser degree."