Does Red Light Therapy Improve SAD?
Seasonal Affective Disorder (SAD) is also known as the “winter blues” or “seasonal depression.” In the simplest terms, it is depression that follows a season pattern, usually occurring in the winter. SAD is considered a variant of Major Depressive Disorder or Bipolar Disorder, rather than a distinct condition. It is recognized in the Diagnostic Manual of Mental Disorders (DSM-5) and affects around 5% of US adults. January and February are the hardest months for people with SAD.
The seasonal nature of SAD and its high prevalence during the winter months, along with resolution during warmer, sunnier seasons, suggests a causal relationship with sun and light exposure. Human biology is clearly linked with the rhythm of the sun, with people naturally following a sleep/wake cycle that is associated with night and day. This is called the circadian rhythm.
Different types of light are known to have variable effects on the circadian rhythm. Both bright white and blue light suppress the release of melatonin, which promotes wakefulness. Blue light exposure can cause the circadian rhythm to shift even when applied later in the day, unlike bright white light which is more effective at causing a shift in the morning. Red light does not suppress melatonin levels or cause the circadian rhythm to shift. These variable effects of different wavelengths (colors) of light have important implications for light therapy, which is the application of external light sources to affect biology.
Light therapy is widely accepted as a first line non-pharmacological treatment for SAD. Usually, this involves treatment with bright light (called Bright Light Therapy, BLT), which delivers very bright light (most often white, but sometimes blue) shortly after waking. BLT has been found to effectively reduce the symptoms of SAD, although white light shows more effectiveness than blue light. A meta-analysis published in 2015 found that bright white light therapy was effective, although the effects were weaker at some time points. A meta-analysis of bright blue light therapy for SAD did not find it to be beneficial.
BLT only partly mimics the natural effects of sunlight, since it delivers only visible light. Bright white light does not include light in the UV spectrum of the sun. This is done intentionally, since UV rays are the component of solar radiation that are the main culprits in causing skin cancer. Bright white light also does not include light in the infrared spectrum of the sun. This omission is less justified, since infrared light does not have harmful effects on the skin (quite the opposite, in fact), and infrared light makes up a significant amount of natural sunlight. BLT that uses blue light excludes not only UV and infrared light but also the non-blue wavelengths of light, including red, orange, yellow, green and violet.
Interestingly, there are no clinical trials of red light therapy to treat SAD, but there are many that have been done looking at the effects of red light on non-SAD depression. All of the non-SAD clinical trials of red light therapy used near infrared light applied directly to the head. A 2022 systematic review concluded that near infrared light therapy “can be classified as strongly recommended for moderate grade of major depressive disorder.” Similarly, a 2023 meta-analysis concluded that there is a “promising role of [near infrared therapy] in the treatment of depressive symptoms.” These results demonstrate that red light therapy has positive effects on mood.
Increased exposure to outdoor light is associated with reduced risk of major depression and greater happiness. Since outdoor light is a combination of visible light (including blue and red), infrared, and UV light, this contrasts with the light used in BLT, which includes only white visible light or blue monochromatic light. With so many studies showing a benefit to using red light therapy (especially infrared light), it is possible that the addition of red light in the treatment of SAD could be beneficial.
We recommend the following practice:
Shortly after waking, use a red light therapy panel (that delivers both red and near infrared light) for 10 minutes, sitting comfortably 6 to 12 inches away. If you prefer, or if it’s uncomfortable to keep your eyes open in front of the red light panel, you can close them – light still penetrates through to the retinal ganglion cells. However, it is safe to open your eyes as long as your red light panel is low to moderate intensity. The 10 minutes spent in front of the red light panel provides a great opportunity to work on breathwork or mindfulness, which have positive effects on mood.
After 10 minutes of red light therapy, use a light box that delivers white light (preferably using warm fluorescent bulbs, which have a lower blue light hazard ratio) for 20 minutes. It is possible to do normal activities while in front of the light box, so people usually set them up in an office (so that they can work on a computer or read) or on a kitchen island. I recommend setting it up in an office space and spending that 20 minutes engaged in an activity that generates a positive mood. For most people, this means avoiding reading the news, but you can do things like sending emails to friends or reading something uplifting. Taking time to be calm and to orient your attention in a positive direction uplifts mood.
Avoid bright light, especially blue light, at night. Exposure to blue light (especially bright blue light) is disruptive to sleep, which is why it is not recommended to use electronic devices (like iPads or e-readers) that emit blue light at night. Keep household lighting dim in the evening and at night. Red light therapy may also be used at night, although you should position yourself farther from the panel so that the light is less intense. Red light panels can even be used as a source of evening/nighttime illumination. Red LED light bulbs may also be used as a source of illumination at night.
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