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Red Light Therapy for Seasonal Affective Disorder

What is Seasonal Affective Disorder (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 symptoms of SAD are similar to the symptoms of non-SAD depression, and include:

SAD occurs at a specific time of year and the diagnosis requires that it recurs at least two consecutive years in the same season. Symptoms last for around 4 to 5 months, and there is full remission of symptoms when the season ends. SAD usually occurs in the Fall or Winter. Risk factors for SAD include being female, living at a northern latitude, a family history of SAD, and being between 18 and 30 years of age.

Both pharmacological and non-pharmacological treatments have been identified as first line therapies for SAD. Pharmacological treatments include antidepressant medications, such as selective serotonin reuptake inhibitors. Non-pharmacological treatments include cognitive behavioral therapy and light therapy. The goal of light therapy is to compensate for the loss of natural sunlight during the shorter and darker winter months, and most often involves exposure to bright white light. 

What is the relationship between light and 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 sleep/wake cycle is also known as our circadian rhythm. Circadian rhythms are the “physical, mental, and behavioral changes an organism experiences over a 24-hr cycle.” In addition to light and dark, circadian rhythms are also influenced by temperature, diet, exercise, stress, and social environment. Light, however, is the primary regulator, and it exerts this influence through effects on the brain.

The influence of light on the brain starts with the eyes. Light enters the retina and activates cells called intrinsically photosensitive retinal ganglion cells. Retinal ganglion cells are active even in people who are completely blind, who show similar sleep and wake cycles to sighted people because of the response of these cells to light. Retinal ganglion cells show their greatest response to the blue light spectrum. Sunlight contains blue light, in addition to many other wavelengths of color.

From the eyes, a signal is sent to the suprachiasmatic nucleus in the brain. Known as the “master circadian clock”, the suprachiasmatic nucleus is the most important circadian regulator. The clock in turn sends out many signals that regulate a wide range of processes in the body, including controlling the expression of up to 10% of our genes. Light is the primary regulator of this internal clock, although there are other non-light influences on this rhythm too.  

Melatonin and cortisol are the main hormonal mediators of the circadian rhythm, and the synthesis of both is regulated by light. Melatonin is secreted in response to the absence of light, triggering sleep. Cortisol is secreted in response to the presence of light, triggering wakefulness. The synthesis of both melatonin and cortisol is controlled by signals that come from the suprachiasmatic nucleus. 

In the winter months, decreased exposure to light causes the circadian rhythm to shift later in the day, which results in a misalignment between the sleep-wake cycle and the circadian rhythms’ natural processes. Exposure to certain types of light on winter mornings pulls the circadian rhythm back into alignment. 

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.

Exposure to light has been clearly shown to be associated with mood. A study of over 400,000 people showed that increasing exposure to daylight associated with reduced risk of major depression and greater happiness. This may be mediated by serotonin, which is known as a “natural mood booster”. Serotonin is a critical link and regulator of both the circadian rhythm and mood, and levels increase with sun exposure. In contrast to the positive mood effects of sunlight exposure, exposure to artificial light later in the day can have adverse effects. In simple terms, the naturally stimulating effect of white and blue light on wakefulness is helpful in the early part of the day but is harmful in the evening and at night. 

The associations between light and levels of melatonin, cortisol, and serotonin provide clues as to how the dark, short days of winter can negatively impact mood. And while more research is needed to clearly understand the pathology of SAD, its positive response to light therapy suggest that light is one of the most important mediators. 

How is red light therapy for Seasonal Affective Disorder used?

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), but dawn simulation is also used. Dawn simulation delivers light that gradually increases during the last half hour of sleep, while BLT delivers very bright light (most often white, but sometimes blue) shortly after waking. Bright light therapy has been shown to be more effective for people with more severe depression, but both are beneficial.

As already described, retinal ganglion cells in the eye respond to light, particularly in the blue spectrum. White light contains all visible light frequencies, including blue, and both white and blue light promote wakefulness, in part through suppression of melatonin. This is why white and blue light are the main sources of light used in SAD light therapy.

Light intensity is measured in Lux, and bright light is typically considered to be at least 10,000 Lux. Light intensity varies greatly, sometimes in surprising ways. Here are some light intensities under different conditions:

In BLT, an external light source (usually called a “light box”) is used that delivers light at around 10,000 Lux. It is recommended to use BLT in the early morning shortly after waking for approximately 30 minutes. The person should position themself 60-80cm from the light box, with the light at eye level. Lower intensity light can be used (2,500 – 5,000 Lux) but with lower intensity light the treatment duration is extended to 1 to 2 hours. Treatment should be done until the season ends.

Light used in BLT will be delivered by either fluorescent or LED lights. Fluorescent lights deliver white light, either warm or cool, while LED lights can deliver both white and blue light. White light is referred to as “colorless daylight” and is made up of all the frequencies in the visible light spectrum (including red, yellow, green, blue, etc.). White fluorescent bulbs and LED lights will also contain all of the visible light frequencies but they can vary in their spectral characteristics, such as the particular wavelength distribution and intensity. 

When the spectrum of light from bright light devices is analyzed, it varies depending on the light source. Fluorescent lights, both warm and cool, emit light that shows several peaks that correspond to different colors, including red. White LED diodes usually have a sharp blue peak, but they also contain wavelengths of different colors. The main difference between white and blue BLT devices is that white light contains multiple colors (called polychromatic), even though it appears white or colorless, while blue light is a singular color (called monochromatic). 

It is sometimes claimed that SAD light boxes provide a “hefty dose” of blue light. This is not entirely true. The spectral analysis of devices that use both warm and cool fluorescent lights reveals a mixture of wavelengths (yes, including blue), but their calculated “blue light hazard” level is actually quite low. Warm fluorescent light is a bit better than cool fluorescent light, which showed around the same blue light hazard as white LED light. It’s also important to note that blue light is “disruptive” to the circadian rhythm precisely because our bodies are naturally designed to respond to the blue wavelengths of light from the sun. When used in the morning, exposure to blue light (even artificial) provides a cue for the system to wake up. It should go without saying that bright light therapy devices should not be used in the evening.

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. 

How Does Seasonal Affective Disorder Relate to Different Wavelengths of Light?

SAD is related to the lack of daylight, or sunlight, during winter months. Sunlight consists of solar radiation, which is energy that is transmitted in the form of waves or particles. The spectrum of light in our environment consists of both light we can see (visible light) and light that our eyes can’t perceive (invisible light). This is called the electromagnetic spectrum. The visible light spectrum is quite narrow, consisting of wavelengths that range from 400 to 700nm and span from violet to red in color.

Although the amount of solar radiation is not constant, approximately 40% percent of the light from the sun is visible light, which can be divided by color and wavelength. Near infrared light waves lie just beyond the “red” end of the visible light spectrum, so we don’t see them. Near infrared light is part of the “infrared” spectrum, which consists of both near infrared and far infrared light. Infrared light makes up 50% of the solar radiation that reaches the earth. The remaining 10% of the light from the sun is also invisible, falling just beyond the opposite “violet” end of the visible spectrum to IR. This is called ultraviolet light (UVL). 

What this means is that 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. 

Does Red Light Therapy Improve Seasonal Affective Disorder?

Red and near infrared light therapy is the application of artificially generated light in the red and near infrared spectral bands. The term “red light therapy” usually describes the use of both red and near infrared light, although only the red light produced by the device is visible to the naked eye. Infrared light can still be perceived by the body as heat when it contacts skin. Like BLT, red and near infrared light therapy does not involve the use of UV rays. The red light used in light therapy usually ranges from 600 to 700 nanometres (nm), with the unit nm referring to distance the light wave travels in one cycle. The near infrared light used in light therapy usually ranges from 800 to 1100nm. 

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.

Another challenging symptom of SAD is sleep disturbance, which is another issue that red light therapy has been found to help. Application of red light therapy during wakefulness improves sleep quality in people with cognitive decline, Guillain-Barré Syndrome, fibromyalgia and stroke. Interestingly, sleep duration decreased with full body red light therapy in elite athletes, while other parameters such as exercise recovery improved. When red light therapy is applied during sleep, there is an increased clearance of waste products from the brain and improved flow of cerebrospinal fluid, which are required for optimal brain health. So, red light therapy is beneficial when applied when either awake or sleeping, and the benefits relate more to improving sleep quality and physiology, rather than to increasing sleep duration. 

As already described, 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. 

Combining Bright and Red Light Therapy to Improve Seasonal Affective Disorder

Red light therapy can easily be combined with BLT in the treatment of Seasonal Affective Disorder. Since the rising sun appears red when first coming up over the horizon, exposure to red light followed by exposure to BLT is recommended. This is a practice that I’ve been doing for several years, following decades of winter seasons in which I suffered from some degree of seasonal depression. Initially, my doctor recommended that I purchase a fluorescent light box, which I used successfully for a few years. After gaining knowledge of red light therapy, I combined the two and now use them in tandem. 

My recommended practice is as follows: 

  1. 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.
  1. 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.
  1. 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. 


We often hear the recommendation by health experts these days to “view morning sun” as a way to optimize health, including mental health. While it is no doubt ideal to have exposure to natural light in the morning, for people that live in cold winter climates this can be very difficult.

Under these circumstances, light devices – both bright and red light – can be used to mimic sunrise and sun exposure.

Although the combination of bright and red/near infrared light has yet to be subject to intensive research, there is strong evidence that both exert a positive influence on mood. Since daylight consists of a combination of light wavelengths, including near infrared light, there is good reason to believe that these two may work in tandem as a powerful tool in the prevention and treatment of Seasonal Affective Disorder.

Dr. Genevieve Newton, DC, PhD  spent close to 20 years as a researcher and educator in the field of nutritional sciences before joining Fringe as its Scientific Director. Gen’s job is to “bring the science” that supports Fringe’s products and education. She is passionate about all things Fringe, and is a deep believer in healing body, mind and spirit using the gifts of the natural world. 

The contents in this blog; such as text, content, graphics are intended for educational purposes only. The Content is not intended to substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your healthcare provider.

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