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Harvard Commentaries
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School

Minding Your Mind Minding Your Mind

Coping with Darker Times -- Treating Seasonal Affective Disorder

October 23, 2012

By Michael Craig Miller M.D.

Harvard Medical School

Here in Boston, the last few autumns and winters have been unseasonably warm. Some of us worry about climate change and others simply enjoy the extra coat-free days. But, no matter what the temperature, it's still dark at 5:00 p.m. And that, to many of us, feels lousy.

For some of us, the lousy feeling is a sign of seasonal affective disorder or SAD. Significant mood changes occur that can't be dismissed with a shrug. The most common form of this disorder tends to start in the fall and gets worse in January and February. Relief comes with longer days in the spring.

About half a million Americans meet diagnostic criteria for SAD. Many more people have milder mood symptoms when the days get shorter. Symptoms may include loss of pleasure and energy, feelings of worthlessness, inability to concentrate, and an uncontrollable urge to eat sugar and high-carbohydrate foods.

As similar medications are used to treat seasonal affective disorder as other mood disorders, we'll focus here on light therapy, which is unique to SAD.

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Standard Light Therapy

Bright white light therapy has been used to treat seasonal affective disorder since the mid-1980s. It involves sitting close to a fluorescent light box for 30 minutes, usually in the morning on waking. The light is much more intense than an ordinary light bulb. Proper light boxes provide 10,000 lux. (The "lux" is a measure of light intensity. By way of comparison, indoor light is about 100 lux, while a bright sunny day is 50,000 lux or more.)

Bright white light acts on cells in the retina that connect to the hypothalamus, a part of the brain that helps control circadian rhythms. These rhythms are thought to be disrupted in seasonal affective disorder.

Research shows that light therapy is as least as effective for treating seasonal affective disorder as is antidepressant therapy.

Although it is a mainstay of treatment, researchers have been looking for ways to improve and refine it because:

  • It doesn't work for everyone. Studies have reported that 50% to 80% of patients with SAD get significant relief from depressive symptoms after bright light therapy. But that still leaves many patients who don't find it helpful.


  • Successful treatment may depend on carefully individualized timing and dosing of light. The light dose depends on the strength of the light source, the patient's distance from the light, light wavelength and duration of exposure. The recommendation for 30 minutes of daily exposure to 10,000 lux is based on average response to white light; some patients may not need that much exposure to benefit. Other people, such as parents of toddlers, may not be able to sit in front of a device for 30 minutes each morning.


  • Some people don't tolerate bright light. The biggest psychological risk is that bright light therapy may trigger hypomania or mania in patients with bipolar disorder. Mood-stabilizing medications can be given to reduce that risk.


  • Bright light can cause retina damage, although it's rare. Some medications can increase the risk, including some antipsychotic medication, lithium, melatonin and St. John's wort. A few medical conditions can also increase risk: People with diabetes or pre-existing retina disease should discuss their conditions with their doctor before trying bright light therapy.

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Enhancing Light Therapy

Researchers are looking at ways to improve the response or reduce the risk of side effects like mania or retinal damage.

Better timing

Abnormal sleep rhythms are common in depression. The hormone melatonin, which helps regulate the cycle of waking and sleeping, may play a role in SAD.

The brain makes melatonin and usually produces more of it during the early evening. The timing of this surge varies from person to person. Some experts believe that, to optimize light therapy, it should be calibrated to a person’s nightly melatonin surge.

Dawn simulation

In this variation of light therapy, a preset light device turns on before a patient wakes up. Light intensity increases gradually from 0.001 lux (equivalent to starlight) to 250 or 300 lux (similar to sunrise) over a period of 90 minutes. Some small studies have found promising results with this technique.

Blue light

Traditional devices use white light, a mixture of all the colors (such as blue, green and red) in the visible light spectrum. The use of light-emitting diode (LED) technology has made it possible to create smaller and more portable devices, and to test specific wavelengths of light.

Ganglion cells in the retina are particularly sensitive to blue light. This suggests that this wavelength may powerfully affect circadian rhythms. Researchers working in this area have begun to find evidence that lower intensity blue light (750 lux) is as effective as bright, full- spectrum light (10,000 lux). If this evidence holds up, it may be easier to provide this light through general lighting fixtures. It may also reduce the risk of side effects or discomfort.

Blue light may have its own special risks, since some wavelengths of blue light may cause retinal damage.

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What You Can Do Today

Experts recommend that patients with seasonal affective disorder first try traditional bright white light therapy after awakening. If it does not help or it creates bothersome side effects, it may be worth trying antidepressants or one of the alternatives under investigation. Since some people with SAD may be experiencing a variation of bipolar disorder, it's worth considering treatments for that disorder.

Although light treatment is relatively safe, there are a few cautions if you want to try it.

  • Discuss your mood problem with your doctor, who may advise you to see a mental health professional before trying light therapy.


  • The U.S. Food and Drug Administration does not test, approve, or regulate light box devices.


  • Before buying any light box, consider asking about wavelengths (to avoid wavelengths that might be harmful) and check to see if it has been used in any reputable research facilities.


  • Before investing your money and time pursuing bright light therapy, work with a professional who is qualified to make a diagnosis, in order to evaluate your individual situation, and to determine whether a diagnosis of seasonal affective disorder is correct.


  • Depression has many causes and there are many good ways to treat it. Review all your treatment options. Establish a relationship with a professional who can help you periodically review your progress.

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Michael Craig Miller, M.D. is editor-in-chief of the Harvard Mental Health Letter and an assistant professor of psychiatry at Harvard Medical School. Dr. Miller has an active clinical practice and has been on staff at Beth Israel Deaconess Medical Center for more than 25 years.

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