Practical Aspects of Light Therapy
In general, it is best to begin light therapy with the patient receiving 10,000 lux. Lower intensities are effective but take significantly more time out of each day. It is usually preferable for patients to obtain commercially available fixtures. Attempts by patients to construct their own fixtures may result in fixtures that put out the wrong amount of light or are electrically unsafe. Commercially available fixtures have additional advantages, such as special ballasts that minimize flicker and features that minimize the transmission of UV rays. Some patients have found a portable head-mounted light device to be useful, but controlled trials demonstrating clear efficacy are still needed (Rosenthal 1998).

Duration of treatment, like dosage of an antidepressant medication, may need to be adjusted according to the needs of the individual patient, the time of year, and the amount of ambient light.

These factors are best considered collaboratively with the patient, who gradually becomes more educated as to his or her need for light. Thirty minutes is frequently a good duration to start with—enough to induce some antidepressant response but not so much as to cause side effects. Although some patients may experience an immediate beneficial effect of light, either activation or a lessening of anxiety, most patients take 2-4 days to register a sustained antidepressant response (Rosenthal et al. 1984). The response to light may be manifested over several weeks (Bauer et al. 1994; Eastman et al. 1998), and a lack of response within the first week cannot be taken as a definitive indication that a patient will not derive any benefit from light over the long run. Light treatments can be administered in divided doses, and some patients report this to be more effective and convenient than when treatment is consolidated in a single block at one time of day.

Several researchers, seeking predictors of response to light therapy, have found a history of hypersomnia, a preponderance of atypical vegetative symptoms, and increased intake of sweet foods in the afternoon to be predictors of a favorable response to light treatment (Krauchi et al. 1993; Oren et al. 1992; M. Terman et al. 1996). As much as 40% of the variance in the antidepressant response to light therapy may be accounted for by hypersomnia alone. Another clinical predictor of a favorable response is a history of reactivity to ambient light. For example, observations of mood improvement following trips south in the winter or varying depths and durations of winter depressions experienced when living at different latitudes would suggest a favorable response to light therapy.

Side effects of light therapy include jumpiness or jitteriness, headache, and nausea, although some nondepressive physical complaints (such as poor vision and skin rash or irritation) may improve with light therapy (M. Terman and Terman 1999). At times, hypomanic syndromes may occur. Full-blown manic responses have been described more frequently among patients with depression that is not seasonal than among those with SAD (Kripke et al. 1986, 1989). All side effects are generally diminished by decreasing exposure to light, either by decreasing duration or by suggesting that the patient sit farther away from the light source. Insomnia may be most pronounced when light therapy is administered at night, and it may be obviated by moving light treatment to an earlier time of day. Damage to the eyes has been discussed as a potential side effect, as noted above, although it has not been reported to date after properly supervised light therapy, even among patients who have been treated for several years (Schwartz et al. 1996). A good history of any eye-related problems should be taken before starting a patient on light therapy (M. Terman et al. 1990). At this time there are no data to suggest specific guidelines for how frequently the eyes should be examined in patients being treated with light therapy.

Clinical experience suggests that light therapy can be combined with antidepressant medications to good effect. Although such combinations have not yet been formally tested, this strategy often permits the use of lower doses of medications, which results in fewer side effects.

Conclusions
Light therapy is widely regarded as useful for patients with SAD. Furthermore, there is evidence that it may prove to be a versatile form of treatment, useful also in persons with other types of mood disorders and persons with sleep and eating disorders. Light therapy may be used either alone or in conjunction with medications. It can be titrated like a medication, both with regard to dosage (duration and intensity) and timing of administration. Our understanding of light therapy and of the techniques and technologies involved in administering such therapy has advanced significantly over the past 20 years. There is every reason to expect that such progress will continue.

Many resources exist to keep interested clinicians and researchers up to date. These include a professional society, the Society for Light Treatment and Biological Rhythms (http://www.sltbr.org), and commercial companies that distribute light therapy devices and information about them. For further information the reader is referred elsewhere.

References