Phototherapy for Seasonal Affective Disorder

Lilian White, MD
October 13, 2025

Seasonal affective disorder (SAD) is characterized by depressive symptoms that occur only during a specific time of year. Symptoms are usually present during the fall and winter, and patients experience full relief of their symptoms during the spring and summer. Less commonly, patients may be affected during spring or summer and experience remission during the rest of the year. Approximately 0.5% to 2.4% of the population in the United States experiences SAD.

The pathophysiology of SAD is complex and incompletely understood. Hypotheses include disruption of the hypothalamic-pituitary-adrenal axis, circadian rhythm, melatonin secretion, or the subsequent results on neurotransmitters to negatively affect mood.

Phototherapy uses indirect light exposure to treat SAD. The mechanism through which phototherapy treats SAD is not fully understood; however, it appears to influence the circadian rhythm. Phototherapy does not appear to improve symptoms through suppression of melatonin production.

Phototherapy, alone or in combination with other treatment options, is recommended as first-line treatment for SAD. Phototherapy includes bright light therapy (ie, treatment with a light box) and dawn simulation. For bright light therapy, patients should be exposed to a lux (ie, brightness) between 2,500-10,000 for 30 to 60 minutes at the same time every day in the morning, ideally just after waking. Suitable light sources cost between $25 and $100 and may be covered by health insurance for patients with a SAD diagnosis. Patients are generally encouraged to face the light source without staring at it so their eyes receive indirect light exposure. Patients may complete activities such as eating, reading, or exercising during phototherapy treatment. A meta-analysis of randomized controlled trials reports bright light therapy is an effective treatment for SAD; however, studies are typically smaller and could be of higher quality.

Dawn simulation uses lower levels of light intensity (eg, 250 lux) and is timed to begin 30 minutes before the patient waking. Benefits of dawn simulation include ease of use (it automatically turns on, reducing risk of missing treatment), perception of a more natural effect by patients, lack of time commitment, and reduced eyestrain due to brightness (compared with bright light therapy). Dawn simulation appears to be similarly effective compared with bright light therapy in patients with mild to moderate symptoms; bright light therapy may be more effective (or perceived as more effective) in patients with more severe symptoms.

The most effective form of visible light appears to be white light (eg, vs blue, green) according to a recent systematic review and meta-analysis.

Caution is encouraged in patients with photosensitive conditions; however, the brightness of bright light therapy is much less than that of midday sun, which is about 50,000 lux. Additionally, bright light therapy devices typically filter out ultraviolet light. It is recommended that patients with eye disease discuss bright light therapy with their ophthalmologist before treatment.

Bright light therapy may also be considered in the treatment of nonseasonal depression. Although bright light therapy may plausibly be considered for the treatment of sleep problems and dementia in older adults, research is currently lacking. Bright light therapy may also be considered as a preventive measure in patients with known SAD. An article in American Family Physician outlines additional treatment options for SAD.