A Guide To Light Therapy For Seasonal Affective Disorder

Have you considered clinical trials for Seasonal affective disorder (SAD)?

We make it easy for you to participate in a clinical trial for Seasonal affective disorder (SAD), and get access to the latest treatments not yet widely available - and be a part of finding a cure.

What is seasonal affective disorder?

Seasonal affective disorder (SAD) is a type of depression characterized by a seasonal recurrence. These depressive episodes present at the same time every year, normally in the winter or autumn seasons. 

It’s commonly referred to as the winter blues and differs from regular depression as symptoms resolve during the summer season. 

It’s a significant mental health issue, accounting for approximately 11%¹ of all cases of depression, and requires treatment to prevent worsening of symptoms. 

Studies have shown that it affects around 0.4% of the US population² and up to 2.9% in Canada¹. Interestingly, women are around four times³ more likely to be affected than men. 

Thankfully, there are several treatments available for people struggling with SAD

What causes seasonal affective disorder?

The specific cause of SAD has not been identified. Underlying factors may include variations in levels of sunlight in different seasons, disruptions in the natural sleep-wake cycles (referred to as the circadian rhythm), low levels of serotonin, and excess melatonin. 

Vitamin D levels also tend to be lower in the winter months (due to a lack of sunlight). Low levels of vitamin D⁴ are associated with poor mood, depression, and an increased likelihood of SAD.

Light therapy is often used for people with the seasonal affective disorder to increase vitamin D levels. 

Symptoms of seasonal affective disorder

People suffering from SAD typically report symptoms similar to depression

People who suffer from SAD struggle to adapt to the change in seasons, which ultimately affects their daily life in ways such as having a reduced ability to work, difficulty maintaining relationships with friends and family, and withdrawing from social activities.

The most common symptoms include: 

  • a decrease in pleasure or interest 

  • social withdrawal

  • reduced energy

  • feeling sluggish 

  • a sense of worthlessness or hopelessness

  • difficulty concentrating

  • repeated thoughts of death or dying

  • indecisiveness

  • feeling guilty

  • depressed mood and increased feelings of anxiety

Less common symptoms include:

  • increased appetite, binge eating, or craving carbohydrates

  • weight gain

  • excessive tiredness or lethargy

  • hypersomnia (excessive sleepiness)

  • decreased appetite in some cases

Symptoms differ, and not everyone experiences all of the symptoms listed. Symptoms can be debilitating and severely impact motivation in many areas of life. 

Early treatment is vital and has been shown to significantly help people suffering from SAD improve their mood, increase energy levels, and get their lives back on track. 

Light therapy is one of the most effective solutions, with some studies⁵ reporting it as being vital for some people to manage their symptoms of SAD.

How does light therapy help with seasonal affective disorder?

Light therapy is the primary treatment for people with SAD and in the majority of cases, people show a significant reduction in symptoms. 

Light therapy involves the use of bright artificial light to make up for the lack of available natural light, which is a factor in some cases of SAD. The increased light helps regulate circadian rhythms. 

Treatment involves sitting in front of a specific light box each day for around 20–60 minutes. Many experts recommend a duration of 30 minutes; however, this depends on the intensity of the light box. 

Light therapy should be performed daily from autumn to spring, with the best results achieved during morning⁶ use.

Light therapy has been shown to work well in combination⁷ with other treatment measures such as exercise. It’s an inexpensive and effective treatment for SAD, without any major side effects. 

Light boxes can be purchased without a prescription, but medical advice should be sought before commencing light therapy as it may not be suitable for people taking certain medications or those with eye disease.  

Research⁸ has found that light therapy could be an effective alternative to antidepressants and may also be used in conjunction with such medications for the greatest benefit; however, more studies are required to verify this. 

How light therapy works

Since SAD usually occurs at times of the year when less sunlight is available, it makes sense that more light exposure should reverse the effects of the disorder. Light therapy functions by activating cells in the retina (a thin layer of tissue that covers the back of the eye). 

These cells are connected to the hypothalamus, a brain region involved in regulating circadian rhythms and the sleep-wake cycle. 

Activating these cells causes glutamate (a neurotransmitter) to be released. Glutamate works by regulating melatonin to encourage sleep and the timing of its release is kept in synchrony by external signals such as light. 

If the hypothalamus is stimulated at a specific time each day, it can reestablish normal sleep-wake rhythms and reduce or eliminate seasonal effects. 


Medical professionals⁸ tend to use fluorescent light boxes with light intensities that are more than 2,500 lux, with the standard dose being 10,000 lux.

To put that into perspective, a bright indoor room is less than 500 lux, whereas a sunny day can be between 50,000 to 100,000 lux. The lower the lux amount, the longer you will need to sit in front of the light box.

Guidelines for bright light therapy:

  • Fluorescent white light is used at an intensity of 10,000 lux, with no ultraviolet wavelengths, or an ultraviolet filter.

  • It is important that the eyes are kept open, but are not staring directly into the box. This means that you can do other activities during the session, such as reading, writing, or eating.

  • Treatment can last about 30 minutes per day, usually in the mornings. Undergoing light therapy sessions in the mornings has been shown to be significantly more effective at treating SAD. This means you should aim to do your daily session as soon as possible upon waking. 

  • Maintain a correct distance to the source of the light⁹. This will differ depending on the type of light box used. Refer to the manufacturer’s guidelines for safe usage. Applications are available on cell phones that can measure lux intensity and inform the user that they are receiving the correct intensity from the light box. 

  • It is important that treatment be continued for the duration of winter or for the whole season where you normally experience symptoms. As soon as light therapy is stopped, symptoms can return within a matter of weeks.

  • You should evaluate your response to light therapy after 2 to 3 weeks of treatment.

  • If your symptoms stop, the dosage should be adjusted for the remainder of the winter season. This could include reducing the time in front of the light box or the frequency of sessions.

  • Treatment can start before winter in following years in order to reduce the chance of SAD returning.

  • You should take care if you feel ‘too high’ or manic after treatment. In this case, you should consult your doctor.

  • Expert medical guidance should be sought prior to treatment for those with bipolar disorder.

How beneficial is light therapy?

An analysis of multiple studies¹⁰ looking at the efficacy of light therapy found it to be significantly more effective than a placebo treatment at reducing symptoms for people affected by SAD. 

Some literature¹¹ states that light therapy can benefit around three-quarters of people with SAD. 

Studies using light therapy¹² have found it to be at least as effective at resolving symptoms as treatment with antidepressants, but the research is inconclusive¹⁰. An investigation found light therapy to be equally effective¹³ at relieving symptoms as cognitive behavioral therapy. 

Other studies have shown that bright light therapy is very effective in the short term¹⁰ but evidence to confirm how beneficial it might be in the long term and to prevent further episodes is lacking. 

One study⁵ reported that the effects of light therapy were strong and relatively quick. 

People described the treatment as ‘a radical, sudden and profound transformation’, with changes in symptoms observed within the first week. However, this study was performed using special in-clinic light rooms, which differ slightly from in-home light boxes. These light rooms are only offered in some Scandinavian countries. 

Light therapy doesn’t resolve symptoms in everyone suffering from SAD. In some cases, other therapies are required, such as cognitive behavioral therapy.

How safe is light therapy?

Light therapy is suitable for most people and symptoms have been shown to improve in a matter of weeks. However, some side effects may occur. 

Side effects are usually minor and include:

  • Blurred vision

  • Feelings of nausea

  • Headache

  • Appetite changes

  • Agitation

  • Eyestrain

These concerns usually go away after a few days of using the treatment or you can improve them by sitting further from the light source or reducing the length of each session. 

Caution should be taken for those with photosensitive skin. In addition, usage at night can affect normal sleep patterns. 

Purchasing a light box

Light boxes can be purchased online without a prescription. If you’re considering investing time and money into light therapy, it’s a good idea to work in conjunction with a medical professional. 

They will provide you with advice on which light box is best suited to your condition and ensure the light box you’re purchasing meets clinical recommendations.

Many light boxes that provide the recommended intensity of 10,000 lux are available for purchase online. Unfortunately, many of them do not specify the distance¹⁴ that you should place yourself from the light source in order to receive the full therapeutic benefits of the lamp

This is one reason that medical advice is highly recommended before commencing treatment. 

Although light therapy is a generally safe procedure, there are still a few considerations to think about when purchasing a lamp:

  • Light boxes are not FDA-approved or tested.

  • Lamps should emit fluorescent light, not ultraviolet wavelengths, which can damage the skin and eyes.

  • Ensure its efficacy by researching if the light box is used in reputable locations such as clinics, hospitals, or research institutions.  

Types of light boxes

White (broad spectrum) light boxes:

  • Large light boxes provide a good source of illumination over a large area at the recommended intensity of 10,000 lux. These types of light boxes are similar to what’s used in research studies and most often meet the medical guidelines for therapy.

  • Smaller light boxes: These often produce less intense light and often require you to sit closer to the light source and avoid moving out of the area exposed to light as much as possible. Some people prefer small light boxes due to their convenience as they may be easier to transport and because they take up less space at home.

Other types of light boxes:

  • LED beam units: These emit a higher concentration of light in the blue wavelengths. People have reported relief of symptoms when using LED light therapy, often equivalent to those seen with 10,000 lux lamps; however, more research is needed in this area. The blue light released from LED devices can be hazardous to some people, which outweighs its therapeutic potential. 

The lowdown

Light therapy is the principal therapy for those suffering from SAD and treatment can resolve symptoms for the majority of people. It may not, however, be suitable for everyone. 

It’s important that therapy be conducted only after seeking guidance from a qualified medical professional so any side effects can be monitored and ensure effective usage.

  1. Estimated prevalence of the seasonal subtype of major depression in a Canadian community sample (2000)

  2. Epidemiology of recurrent major and minor depression with a seasonal pattern. The national comorbidity survey (1998)

  3. Seasonal affective disorder: An overview of assessment and treatment approaches (2015)

  4. Vitamin D as a neuroactive substance: Review (2006)

  5. Patients’ experience of winter depression and light room treatment (2017)

  6. Light therapy for seasonal and nonseasonal depression: Efficacy, protocol, safety, and side effects (2005)

  7. Vitamin D and depression: Where is all the sunshine? (2011)

  8. Seasonal affective disorder: A clinical update (2007)

  9. Commercially available phototherapy devices for treatment of depression: Physical characteristics of emitted light (2019)

  10. The efficacy of light therapy in the treatment of seasonal affective disorder: A meta-analysis of randomized controlled trials (2020)

  11. Seasonal affective disorder and seasonality: A review (2000)

  12. The efficacy of light therapy in the treatment of mood disorders: A review and meta-analysis of the evidence (2005)

  13. Randomized trial of cognitive-behavioral therapy vs. light therapy for seasonal affective disorder: Acute outcomes (2021)

  14. Commercially available phototherapy devices for treatment of depression: Physical characteristics of emitted light (2019)

Other sources:

Have you considered clinical trials for Seasonal affective disorder (SAD)?

We make it easy for you to participate in a clinical trial for Seasonal affective disorder (SAD), and get access to the latest treatments not yet widely available - and be a part of finding a cure.

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