Bright light therapy can relieve the symptoms of seasonal affective (and other) disorders. Kathleen Kendall-Tackett looks at how it works. (Part I). Part II: Light Therapy to Treat Depression in Pregnant and Postpartum Women.

Symptoms of seasonal affective disorder (SAD)

Do you dread the change of seasons? Shorter, darker days that occur during the late fall and winter months, as darkness falls earlier and earlier in the day, can lead to:

  • fatigue
  • lethargy, difficulty waking and oversleeping
  • anxiety
  • craving carbohydrates
  • difficulty concentrating
  • depression or a general sense of malaise.

This pattern of symptoms is known as seasonal affective disorder (SAD) and often leads to weight gain according to the National Alliance on Mental Illness (NAMI, 2007).

What is it?

SAD may be an evolutionary adaptation, similar to hibernation. As food gets scarcer and the weather gets colder, animals adapt by storing fat and reducing caloric output. Applied to humans, this could explain our carbohydrate cravings, increased sleep and reduction in energy levels. It might also play a role in reproduction, since it is more beneficial for a woman of childbearing age to conserve resources (Davis & Levitan, 2005; Blair, 2013).

How Bright Light Therapy Helps Seasonal Affective Disorder
John Atkinson Grimshaw 1836-1893

Reduced sunlight during the winter leads to biochemical changes in the brain. Serotonin and melatonin have been linked to changes in mood, energy, and sleep patterns. Low levels of serotonin are associated with depression. Serotonin production is activated by sunlight, so less sunlight can lower levels and lead to depression. Melatonin regulates sleep and is produced in greater quantities in darkness. Higher melatonin levels could cause sleepiness and lethargy as the days grow shorter. The combination of the changes in the levels of serotonin and melatonin could contribute to SAD.

An alternative to medications

Clinicians have used bright light therapy for several decades to successfully treat seasonal affective disorder and as early as the mid-second century (AD), Aretaeus of Cappadocia, one of the most renowned medical scholars of Greco-Roman antiquity after Hippocrates, recommended,

“Lethargics be laid in the light, and exposed to the rays of the sun, for the disease is gloom.”

Light therapy has far fewer side effects than medications and can provide relief within days (NAMI, 2007). Fortunately, safe treatments for pregnant and breastfeeding women are available. In a clinical trial, light therapy was as effective as fluoxetine (Prozac) in relieving symptoms, and patients who received light therapy had an earlier response to treatment with fewer side effects (Lam et al., 2006).

How Bright Light Therapy Can Help Seasonal Affective Disorder
Ken Tackett

Other disorders

Research tells us that light therapy is also helpful for other affective disorders, including:

  • nonseasonal depression
  • antenatal and postpartum depression
  • bipolar disorder
  • some eating disorders
  • certain sleep disorders (Oren et al., 2002; Terman & Terman, 2005).

The American Psychiatric Association indicated that bright light therapy was an effective treatment for both seasonal and nonseasonal depression, and was as effective as medications (Golden et al., 2005).

In addition to medication

Light therapy can also be safely combined with medications in most cases, and can boost the activity of medications in patients who are either not responding or who have had a partial response. Terman and Terman (2005) summarized the results of several clinical trials where patients were given either bright light therapy (10,000 lux) or dim light (2,500 lux) in addition to their medications. They noted that in all of these studies, bright light improved remission rate and sped improvement. A recent randomized clinical trial found that bright light treatment, both as monotherapy and in combination with fluoxetine (Prozac), was efficacious and well tolerated in the treatment of adults with nonseasonal major depressive disorder. The combination treatment had the most consistent effects (Lam et al., 2016).

Light intensity, duration and timing of light exposure

Although a number of light intensities have been investigated, lights with intensities of 10,000 lux, with 30 to 40 minutes of exposure, appear most effective (Terman & Terman, 2005). Two studies with light exposures of 30 to 40 minutes at 10,000 lux achieved a 75% remission rate. It took two hours to achieve similar remission rates with 2,500 lux. And in some cases, even with longer exposure, lower-intensity lights are not as effective (Terman & Terman, 2995).

When longer exposure times are necessary, patients are less likely to comply. This may be particularly true for mothers of young children who probably won’t find it practical to sit for two to three hours in front of a light box.

Mornings are best

Timing of light exposure makes a difference. Exposure to bright light is generally much more successful in achieving remission if it occurs in the morning. Terman and Terman (2005) cited one analysis of 332 patients, across 25 different studies, that compared administration of light in the morning, mid-day and evening. They noted remission rates after one week of treatment, with significantly higher rates in the morning (53%), compared with mid-day (32%) and evening (38%) exposures. According to their analysis, morning light should be administered 8.5 hours after a patient’s melatonin onset.

Because of the effectiveness of morning light exposure, a variant to standard light therapy has recently been added to the repertoire of possible treatments: dawn simulation. As the name implies, dawn simulation refers to a light that comes on before a patient is awake, and gradually increases in intensity over a period of 15 to 90 minutes (the length of the sunrise can be tailored to individual preference). The advantage to this treatment is that it does not require sitting in front of a light box for an extended time, making it a more practical alternative for new mothers or mothers of young children. Although a relatively new technique, it is showing promise as a treatment for SAD (Golden et al., 2005). Some newer lighting devices are both light boxes and dawn simulators.

How Bright Light Therapy Can Help Seasonal Affective Disorder
Ken Tackett

Why is light effective?

A number of possible mechanisms for light’s effectiveness have been proposed. Most explanations have to do with modifying the internal circadian clock. Our circadian rhythms, or daily patterns of sleep and arousal, are regulated by the pineal gland, which secretes melatonin. The pineal gland responds to light via light receptors in the retina. Exposure to light in dark winter months appears to reset the internal clock. The antidepressant effect is stronger when patients are exposed to morning (rather than evening) light. This is likely due to the diurnal variations in retinal photoreceptor sensitivity, with greater sensitivity to morning light. Indeed, exposure to evening light can lead to insomnia and hyperactivation in some people (NAMI, 2007; Terman & Terman, 2005).

One exception to the use of morning light is in patients with bipolar disorder. Morning light exposure can increase risk of a manic episode. This problem can be addressed by timing light exposure later in the day and continuing on medications during light treatment (NAMI, 2007; Terman & Terman, 2005).

Safety issues

Because light boxes can be relatively expensive and appear to be simple, patients often consider assembling a unit themselves. Clinicians generally recommend that patients don’t use homemade devices for several reasons. First, it is difficult for consumers to find lights that are of sufficient brightness to generate a therapeutic effect (despite advertising to the contrary). Second, some patients have experienced excessive irradiation, and corneal or eyelid burns with homemade devices. Finally, homemade devices often use incandescent lights. Some of these have been marketed for bright light therapy but are not recommended because approximately 90% of light output from incandescent bulbs is on the infrared end of the spectrum. Infrared exposure at high intensity can cause damage to the lens, cornea, and retina (Terman & Terman, 2005).

Light boxes with high levels of exposure to ultraviolet (UV) light can cause eye damage, and there is some controversy about the safety of blue lights. Safe light boxes are those encased in a box with a diffusing lens that filters out UV radiation (NAMI, 2007). “Full spectrum” bulbs are not necessarily advantageous and are often expensive. The National Alliance on Mental Illness (NAMI, 2007) recommends bulbs with a color temperature between 3000 and 6500 degrees Kelvin. These have not been shown to cause any harm to patients’ eyes. Only use a lighting apparatus from a reputable dealer (two possible sources listed below). Since price may be an issue, many hospitals, and some manufacturers, have loaner programs that allow patients to try the lighting device in their homes before buying them.


Bright light therapy is a generally safe, well tolerated treatment option for seasonal depression. It may relieve nonseasonal depression as well (Melrose, 2015, Lam et al., 2016). Bright light therapy is also breastfeeding friendly and can be used during pregnancy. Although therapeutic light boxes can be costly at first, a single purchase will last for years. For patients who dread winter, this investment is often well worth the cost. 

And see part II: Light Therapy to Treat Depression in Pregnant and Postpartum Women

Preventing Seasonal Affective Disorder

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Aretaeus: The extant works of Aretaeus, the Cappadocian. F Adams (trans). (1856). London: Sydenham Society.

Blair, H. (NAMI). (2013). Less sunlight means more blues for some. Retrieved from

Davis, C., & Levitan, R. D. (2005). Seasonality and seasonal affective disorder (SAD): An evolutionary viewpoint tied to energy conservation and reproductive cycles. Journal of Affective Disorders, 87(1), 3–10. doi:10.1016/j.jad.2005.03.006

Golden, R.N., Gaynes, B.N., Ekstrom, R.D., Hamer, R.M., Jacobsen, F.M., Suppes, T., Wisner, K.L., & Nemeroff, C.B. (2005). The efficacy of light therapy in the treatment of mood disorders: A review and meta-analysis of the evidence. American Journal of Psychiatry, 162, 656–662. doi:10.1176/appi.ajp.162.4.656

Lam, R.W., Levitt, A.J., Levitan, R.D., Enns, M.W., Morehouse, R., Michalak, E.E., & Tam, E.M. (2006). The CAN-SAD study: A randomized controlled trial of the effectiveness of light therapy and fluoxetine in patients with winter seasonal affective disorder. American Journal of Psychiatry, 163, 805–812. doi:10.1176/ajp.2006.163.5.805

In store

Lam, R. W., Levitt, A. J., Levitan, R. D., Michalak, E. E., Cheung, A. H., Morehouse, R., … Tam, E. M. (2016). Efficacy of bright light treatment, fluoxetine, and the combination in patients with nonseasonal major depressive disorder. JAMA Psychiatry, 73(1), 56. doi:10.1001/jamapsychiatry.2015.2235

Melrose, S. (2015). Seasonal affective disorder: an overview of assessment and treatment approaches. Depression Research and Treatment, 2015, 1–6. doi:10.1155/2015/178564

National Alliance on Mental Illness (2007). Seasonal affective disorder. http://www.nami. org,

Oren, D.A., Wisner, K.L., Spinelli, M., Epperson, C.N., Peindl, K.S., Terman, J.S., & Terman, M. (2002). An open trial on morning light therapy for treatment of antenatal depression. American Journal of Psychiatry, 159, 666–669. doi:10.1176/appi.ajp.159.4.666

Terman, M., & Terman, J.S. (2005). Light therapy for seasonal and nonseasonal depression: Efficacy, protocol, safety, and side effects. CNS Spectrums, 10, 647–663. doi:10.1017/s1092852900019611


American Psychiatric Association

American Psychological Association help center

Mind (mental health charity)

National Alliance on Mental Illness

Rosenthal, N.E. (2006). Winter blues: Everything you need to know to beat seasonal affective disorder, Revised Ed. New York: Guilford. This book is the “bible” of self-help guides on SAD, written by the physician who first documented the phenomenon.

I’ve dealt with both of the two following named companies and have found them to be reputable suppliers of light boxes: The Sunbox Company and

kathleen-kendall-tackett-womens-health-todayDr. Kendall-Tackett is a health psychologist and International Board Certified Lactation Consultant, and the owner and Editor-in-Chief of Praeclarus Press, a small press specializing in women’s health. She is Editor-in-Chief of two peer-reviewed journals: Clinical Lactation and Psychological Trauma. She is Fellow of the American Psychological Association in Health and Trauma Psychology, Past President of the APA Division of Trauma Psychology, and a member of the Board for the Advancement of Psychology in the Public Interest. Dr. Kendall-Tackett specializes in women’s-health research including breastfeeding, depression, trauma, and health psychology, and has won many awards for her work including the 2016 Outstanding Service to the Field of Trauma Psychology from the American Psychological Association’s Division 56.

Dr. Kendall-Tackett has authored more than 400 articles or chapters, and is currently completing her 35th book, The Phantom of the Opera: A Social History of the World’s Most Popular Musical. Her most recent books include: Depression in New Mothers, 3rd Edition (2016, Routledge UK, in press), Women’s Mental Health Across the Lifespan (2016, Routledge US, in press, with Lesia Ruglass), Psychology of Trauma 101 (2015, Springer, with Lesia Ruglass) and The Science of Mother-Infant Sleep (2014, Praeclarus, with Wendy Middlemiss). Her websites are:

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