What is the Dose of Light Therapy for Seasonal Affective Disorder?

Patient Presentation
A 21-year-old female came to clinic during winter college break to refill her acne medications. She said she was doing well in a college located 3 hours away and noted that in addition to her antidepressant medication she was also using her light box daily since the late fall. The health care provider expressed surprise as he was unaware that she was diagnosed with seasonal affective disorder. The student said that she had been diagnosed at her college and had instituted the light therapy the previous winter. She noted a difference in her mood last winter, and therefore she re-instituted the light therapy this season. She said she used the light box during the early evenings when she was studying. The past medical history revealed major depression and seasonal affective disorder. The family history was positive for depression.

The pertinent physical exam showed a happy appearing female with mild comedomal acne primarily on her forehead and some on her back. The physician added the diagnosis of seasonal affective disorder to her medical record problem list. He refilled her medications and reiterated that she could call the office if she ever had questions or concerns even though she was away at college. Later he reviewed some guidelines since he wasn’t sure how the light was dosed.

Seasonal affective disorder was first systematically described in 1984. It can occur at different times of the year but predominantly winter and less commonly summer.
The DSM IV criteria includes:

  • There is a temporal relationship between the onset of major depressive episodes and a particular time of year.
  • Full remissions (or a change from depression to mania or hypomania) also occur at a characteristic time of year.
  • In the last two years, two major depressive episodes have occurred that demonstrate the temporal seasonal relationships defined in the two criteria above and no nonseasonal major depressive episodes have occurred during the same period.
  • Seasonal major depressive episodes substantially outnumber the nonseasonal major depressive episodes that may have occurred over the individual’s lifetime.

Patients with seasonal affective disorder usually have typical depressive symptoms including decreased interest or pleasure, psychomotor retardation or agitation, energy loss, feelings of worthlessness, excessive or inappropriate guilt, decreased concentration, indecisiveness, and recurrent thoughts of death. Most patients with seasonal affective disorder also have “atypical” symptoms including hyposomnia, fatigue, increased appetite and weight gain (often for carbohydrates and sugars that is almost uncontrollable).

Prevalence depends on the population but US rates are around 0.4% and in Canada 1.7-2.9%. The cause is unknown but appears to studies appear to support genetic, neurotransmitter and circadian rhythms as possible causes. Light therapy is effective treatment with response rates from 60-90% in controlled studies.

Learning Point
Lux is an illumination unit. A sunny day is 50,000-100,000 lux or more, and a cloudy winter day is about 4,000 lux. A bright office light is about 100 lux, and indoor light is < 500 lux. The standard dose for treatment is 10,000 lux of white, fluorescent light for 30 minutes per day. Light boxes are usually used to delivery the therapy. A 10,000 lux light box is the usual standard light box but each light box is different (including the intensity and wavelengths). All should have an ultraviolet filter to protect eyes and skin. More recent data appears to support wavelengths nearer to the blue spectrum. The light boxes need to be positioned at the proper distance from the patient and used for the proper amount of time. For example, a light box may deliver 2500 lux at a distance of 15-18 inches for 30 minutes. Therefore the patient should have the light box 15-18 inches away and would need to use it for 2 hours to achieve the 10,000 lux dose. Receiving the light therapy in the morning is superior to later in the day, but light therapy other times of day may be helpful to some patients. Light therapy generally will improve symptoms in a few days with studies often evaluating symptom changes at 1-3 weeks.

Questions for Further Discussion
1. What study instruments can be used to diagnosed seasonal affective disorder?
2. What is the differential diagnosis of seasonal affective disorder?
3. What is the efficacy of using antidepressants and light therapy for seasonal affective disorder?
4. What are the side effects of light therapy?

Related Cases

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at SearchingPediatrics.com, the National Guideline Clearinghouse and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for this topic: Seasonal Affective Disorder

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

Lam RW, Levitt AJ, eds. Canadian Consensus Guidelines for the Treatment of Seasonal Affective Disorder. Clinical and Academic Publishing. 1999.

Westrin A, Lam RW. Seasonal affective disorder: a clinical update. Ann Clin Psychiatry. 2007 Oct-Dec;19(4):239-46.

Shirani A, St. Louis EK. Illuminating Rationale and Uses for Light Therapy. J Clin Sleep Med. 2009;5:155-163.

ACGME Competencies Highlighted by Case

  • Patient Care
    1. When interacting with patients and their families, the health care professional communicates effectively and demonstrates caring and respectful behaviors.
    2. Essential and accurate information about the patients’ is gathered.
    5. Patients and their families are counseled and educated.
    8. Health care services aimed at preventing health problems or maintaining health are provided.

  • Medical Knowledge
    10. An investigatory and analytic thinking approach to the clinical situation is demonstrated.
    11. Basic and clinically supportive sciences appropriate to their discipline are known and applied.

  • Practice Based Learning and Improvement
    12. Evidence from scientific studies related to the patients’ health problems is located, appraised and assimilated.

  • Interpersonal and Communication Skills
    17. A therapeutic and ethically sound relationship with patients is created and sustained.


    Donna M. D’Alessandro, MD
    Professor of Pediatrics, University of Iowa Children’s Hospital