Light Therapy

September 15, 2011

Light therapy, also referred to as phototherapy, has been a unique form of treatment for individuals suffering from a depressive disorder that has seasonal patterns. In the majority of cases, these individuals develop an episode of depression in the fall or winter with remission of the episode in the spring. Light therapy requires that the individual be exposed to a bright artificial light source on a daily basis during the course of treatment.

The mechanism of action is based on the human circadian rhythm, which exhibits two distinct phases, a diurnal phase and a nocturnal phase. The diurnal phase is one of active engagement in the environment with increased body temperature and a decrease or cessation of the secretion of certain hormones including melatonin. The nocturnal phase is one of rest, sleep, a decrease in body temperature, and the augmentation of the secretion of these hormones.

The body’s endogenous pacemaker for the establishment of this rhythm is the hypothalamus. It responds to the changes in light as detected by the retina of the eye. As a result of this light/dark cycle, a “phase-response curve” (PRC) is established. The PRC is a graphic representation of the relationship of light exposure or restriction on the circadian rhythm.


Light exposure in early morning or dawn advances the curve or shifts the rhythm earlier. Light applied at dusk would delay or shift the rhythm later. Light applied in the middle of the day would be predicted to have minimal effect on the circadian rhythm.

In addition to understanding the significance of light and its effect on the circadian rhythm, it is also important to understand the role of melatonin and its effect on animal behavior. The pineal gland, located in the brain, is responsible for the nocturnal secretion of melatonin. The retina shares an axis with the hypothalamus and the pineal gland. Decreased light to the retina, as noted in the diurnal phase, causes secretion of melatonin. The seasonal pattern of animal behavior has been widely studied and has been associated with variations in melatonin secretion. With an increase in nocturnal (night time) secretion of melatonin, as would be expected in the fall and winter months, animals become less active and aggressive, eat less, sleep more, lose interest in sex, and withdraw from the environment. The opposite effect is noted with decreased melatonin secretion which occurs in the spring and summer months.

The most accepted theory for the efficacy of light therapy is based on the observation that exposure to bright artificial light in the morning causes a phase advancement of biological rhythms. This advancement has, in many cases, effectively treated the delayed circadian rhythm associated with major depressive disorders with seasonal patterns. The theory that light therapy works by effecting melatonin secretion has not been adequately supported in the literature.

Although the type of artificial light may vary (artificial bright light vs. fluorescent; green light vs. red light), an artificial light source without ultraviolet radiation with sufficient intensity is recommended for treatment. The more intense light sources, 10,000 lux, have been shown to be superior to less intense ones, 2,500 lux. In addition, the more intense the light source, the less time is required for therapy. Thirty minutes spent in a light box supplying 10,000 lux may be equivalent to 2 hours spent in front of a light source of 2,500 lux. The individual is exposed to the light source within 10 minutes of awakening. Although individuals are cautioned not to stare into the light source directly, occasional glances at the light are necessary to obtain full benefit of treatment. Individuals have reported improvement in depressive symptoms within the first week of treatment. Usually treatment lasts from 10 to 14 days. Artificial bright light is supplied through a light box or with a portable, head-mounted light visor.

Indications for light therapy are in the treatment of mood disorders associated with a seasonal pattern. This disorder is referred to as seasonal affective disorder (SAD). This depressive disorder is seen predominantly in women, affecting up to 80% of reported cases. The mean age of onset is 40 years.

Subsyndromal symptoms, meaning that symptoms are present without having the full syndrome, of SAD, often referred to as the “winter blues,” have also shown response to light therapy. Other disorders have either equivocal results or anecdotal (not established by systematic research) reports of benefits. They include nonseasonal depression, antepartum depression, late luteal phase dysphoric disorder, bulimia nervosa, delayed sleep phase syndrome, early morning awakening, insomnia in the elderly, and jet lag.

Side effects of light therapy have included headache, eyestrain, nausea, insomnia, and hyperactivity or jitteriness.

In conclusion, light therapy has been shown to be of benefit to individuals suffering from a depressive disorder with a seasonal pattern. Other disorders listed above, including nonseasonal depression and antepartum depression, have fewer reported success rates but have also been noted to benefit in some cases.

SEE ALSO: Depression, Mood disorders

Suggested Reading

  • Boulos, A. (1998). Bright light treatment for jet lag and shift work. In R. W. Lam (Ed.), Seasonal affective disorder and beyond (pp. 253—287). Washington, DC: American Psychiatric Press.
  • Eastman, C. I., Young, M. A., Fogg, L. F., et al. (1998). Bright light treatment of winter depression: A placebo-controlled trial. Archives of General Psychiatry, 55, 883—889.
  • Parry, B. L., Gerga, S. L., Mostofi, N., et al. (1989). Morning versus evening bright light treatment of late luteal phase dysphoric disorder. American Journal of Psychiatry, 146, 1215—1217.
  • Schwartz, P. J., Brown, C., Wehr, T. A., et al. (1996). Winter seasonal affective disorder: A follow-up study of the first 59 patients of the National Institute of Mental Health Seasonal Studies Program. American Journal of Psychiatry, 153, 1028—1036.

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