Effect of Light on Health

Physicians have long been advising their patients to seek adequate light as a necessary component of health. However, it wasn’t until very recently that science has been able to show how instrumental bright light exposure can be to maintaining physical and mental health.


In 1984, a seminal paper defining Seasonal Affective Disorder (SAD) described application of bright artificial light for the treatment of winter depression. Dr. Norman Rosenthal and colleagues hypothesized that lengthening the daily photoperiod (in effect, mimicking summer day length in the northern latitudes) would lead to remission of winter depressive symptoms.

Research & Clinical Studies

Since that time, many centers around the world have conducted studies using bright light in various varieties and applications. These studies have refined the clinical issues involved in use of bright light therapy, showing, for example, that it is not necessary to mimic the length of a spring or summer day for a remission of depressive symptoms, but merely to deliver the photic pulse, as short as 30 minutes, to signal a springtime sunrise to the nervous system.

Studies have also been investigated the safety of exposure to bright light therapy and, while found to be safe for most people, those with pre-existing eye abnormalities should undergo this treatment method with periodic eye examinations. 2005 was a signal year for the field, with consensus achieved by an American Psychiatric Association work group that light can serve as a first-line treatment intervention for both seasonal and nonseasonal depression. In other words, we have a viable alternative or adjunct to antidepressant drugs.

Bright Light Therapy and Sleep Disorders

Another area where bright light therapy has proven beneficial is in the treatment of certain sleep disorders. In advanced sleep phase syndrome (ASPS) we see premature sleep onset and early morning awakening. Conversely, in delayed sleep phase syndrome (DSPS) we see difficulty initiating sleep before 1 a.m. (sometimes much later) and an impossible struggle to awaken for a normal workday. These insomnias are often associated with altered circadian rhythms of body temperature and melatonin secretion by the pineal gland. Selective application of bright light therapy in the morning (to correct phase delayed patients) or in the evening (to correct phase advanced patients) has been very effective in “resetting” patients’ internal clock to coincide with normal living schedules.

Future Directions

Future applications of bright light therapy may well include any area where a disease or syndrome recurs seasonally, shows winter exacerbation, or plausibly is related to insufficient or ill-timed outdoor light exposure regardless of the season. Examples of promising research include light treatment for bulimia nervosa and binge eating disorder, depression during pregnancy and premenstrual depression, adult attention deficit hyperactivity disorder, correction of discomfort related to shift work and jet lag, and behavioral disruptions of Alzheimer’s disease including sleep and daytime agitation.