Rosenthal provided guidance for effective light therapy for patients with seasonal affective disorder (SAD). The author is from the National Institute of Mental Health in Bethesda, Maryland.


Patient evaluation prior to initiating:

(1) photophobia or retinal disorders

(2) photosensitivity (albinism, porphyria, drug-induced, SLE, other)


Light prescription for light exposure therapy:

(1) The light intensity should be 10,000 lux.

(2) Ultraviolet (UV) light should be reduced to a minimum, by source of light source and/or use of a light filter.

(3) Full spectrum lights are not required.

(4) The source is pointed at 45° to the patient (allowing reflection) at a distance of 45 cm (1.5 feet).

(5) The patient should read or work during a session, periodically glancing at the light but not staring into it.


Initial dosing: Start for 30 minutes at a convenient time anytime during the day. A session at the end of a long day before retiring may be less effective.


Dose adjustment for inadequate response:

(1) increased duration per session

(2) provide an additional session at another time of the day


It may take several weeks of daily therapy to be effective. Some response should be seen by 4 weeks if it is going to be effective.


In addition a bedside lamp on a timer can be used to shine light on the patient's face towards the end of the sleep cycle, using a lower intensity light (250 lux).


Light therapy is typically discontinued at the end of the affected season. The patient should plan to reinitiate it when the season starts again.


A patient may be noncompliant because of scheduling problems. This can be addressed by:

(1) shifting the light session to a different part of the day

(2) trying to include a light session while at work

(3) review of schedule to reduce stressors


Possible side effects, which may respond to shorter sessions or moving the light further away:

(1) headache

(2) eye strain

(3) irritability

(4) insomnia

(5) hypomania


Adjunctive therapy, especially if there is evidence of concurrent anxiety and depression:

(1) exercise program

(2) antidepressants

(3) stress management

(4) psychotherapy


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