Light Therapy Box: A Treatment For Seasonal Depression

Seasonal affective disorder (SAD), also known as seasonal depression or the “winter blues,” involves the onset of depressive symptoms during a certain season or time of year, typically in winter. For the rest of the year, a person with SAD has no symptoms.

Light therapy has been used as a treatment for SAD since the 1980s. This form of treatment replaces the sunlight lost during the winter months, reducing depressive symptoms such as sleepiness and boosting your mood. 

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 subtype of major depressive disorder where depressive symptoms arise due to changes to seasonal weather and climate. 

Approximately 5%¹ of people in the US experience SAD. Around 10-20% of people in the US who are diagnosed with depression have symptoms with seasonal patterns¹ typical of SAD. 

The symptoms of SAD tend to last for about 40% of the year² and are absent or infrequent during the remainder of the year.  SAD most commonly occurs during the winter, but about 10% of people diagnosed with SAD experience symptoms in summer.³ 

Causes of SAD

While the exact causes of SAD are unclear, it is thought to be caused by a disruption to the circadian rhythm¹ (biological clock), increased levels of melatonin, and decreased levels of vitamin D and serotonin.

Increased melatonin production

Seasonal affective disorder is directly correlated with an increase in melatonin levels⁴ in the bloodstream. Melatonin is the hormone that regulates sleep. 

The decrease in sunlight during the winter months can increase melatonin production as melatonin synthesis is activated by darkness. The cells in your body that produce melatonin also regulate your biological clock. This increase in melatonin disrupts your biological clock and causes you to feel sleepy, a common symptom of SAD

Decreased levels of vitamin D

Vitamin D is primarily absorbed through exposure to sunlight. During the winter months, there is less sunlight, resulting in there being less vitamin D available to be absorbed by your body. 

Vitamin D is required for the synthesis of serotonin, a hormone in your brain that regulates your mood. If your body does not have sufficient amounts of vitamin D, it cannot make enough serotonin, which can result in the depressive symptoms experienced as seasonal affective disorder. 

Risk factors

Risk factors for developing seasonal affective disorder include: 


Some of the most common depressive symptoms experienced in SAD are similar to those experienced in atypical depression.⁴ In particular, winter SAD is associated with overeating, craving carbohydrates, weight gain, and an increased need for sleep. 

Those who experience SAD in the summer tend to have slightly different symptoms, such as irritability, reduced sleep, and weight loss. 

Other symptoms of seasonal affective disorder include:

  • Low or sad mood

  • Loss of interest in things you previously enjoyed

  • Inattentiveness 

  • Difficulty concentrating 

  • Hopelessness 

  • Social withdrawal

How does a light therapy box help?

Light therapy can help to regulate your circadian rhythm and production of melatonin.⁴ Cells in your eyes sense the light and send a signal to your brain to stop melatonin production, therefore preventing the overproduction of this sleep hormone.

Although light therapy boxes designed for SAD treatment are not damaging to your eyes, it is important to get your eye health checked before starting light therapy. 

Some medications — like St John’s wort — increase your body’s sensitivity to light. If you are currently taking medication, you should talk to your doctor about whether light therapy is right for you. 

Light therapy can be used in combination with antidepressants and other forms of therapy. If you are taking antidepressants, you still may benefit from light therapy for seasonal depression relief. Light therapy can also provide relief from seasonal depressive symptoms if you cannot be prescribed antidepressants..

You may experience a few side effects when you start light therapy. However, these are usually minor and only last for a few days. 

Side effects may include: 

  • Headache

  • Nausea

  • Dizziness 

Selecting the right light box

When choosing a light box to treat your seasonal affective disorder, there are a few factors to consider. Use the following sections as a guide to selecting the right light box for your needs.


The intensity of light needed for light box therapy is between 2,500 to 10,000 lux. It is best to choose a light box with a light intensity of 10,000 lux.⁵ 

This is a higher intensity than normal at-home lighting and it mimics the light intensity of the sky shortly after dawn. This will help to regulate your circadian rhythm when used just after waking up. 

Light boxes with a lower light intensity will require longer treatment sessions to obtain the same benefits as a 10,000 lux light box which can be used for a shorter period of time.

Screen size

When it comes to screen size, the larger the better. Light boxes with a screen size⁶ of 155 square inches — dimensions of at least 11 inches by 15 inches — or larger are ideal for SAD treatment. This is because light intensity decreases with distance. Moving your head slightly during treatment can decrease the dose of light you receive and you may not obtain the desired results. 

The larger the light box screen, the more area the light will cover. This will help to reduce your chances of not receiving enough light during your treatment. 

UV filter

UV rays are harmful to your eyes and are not beneficial in the treatment of SAD.

Light boxes for seasonal affective disorder need to have a UV light filter. Some light therapy products do not have a UV filter, but these are typically used for treating skin conditions, rather than SAD.

Light color

The most beneficial light color for SAD light therapy is a cool white light⁶ with a color temperature under 5000K. Light boxes advertised as “full-spectrum” or with a color temperature over 5000K do not provide more benefits and can cause glare. 

How to use your light box to treat seasonal affective disorder

For the best results, use your light therapy box for 30 minutes shortly after waking. You should start to notice the benefits of light therapy after a few days to two weeks of regular use. 

If you do not notice any positive change in your symptoms after two weeks, try increasing the length of your light box session by 15 minutes every couple of days. 

Consistency is key, so make sure to use your light box at the same time every day to maximize the effectiveness of the treatment. To maintain the benefits, you should continue to use your light box daily during winter, even after symptoms disappear. This will reduce the chances of your symptoms returning. 

It is recommended to not use your light box right before bed as this can disrupt the production of melatonin and disturb your sleep. 

Position your light box above eye level from your seated position and tilt it down towards your eyes. The light box should be about 14 inches away⁷ from your eyes. If your light box has a light intensity that is lower than 10,000 lux, you will need to sit closer to it. 

You do not have to sit still while using the light box. You can read, work, or eat if you choose to, but you must keep your eyes open as this is how light therapy works. However, it is not recommended to stare straight at the light box. 

If you know you will or are likely to experience SAD symptoms during the upcoming seasons, you can start using your light box in the weeks leading up to the season to help prevent or reduce depressive symptoms

The lowdown

Light therapy is a first-line treatment for seasonal affective disorder that occurs in winter. The therapy involves using a light box emitting a cool white light that imitates morning sunlight. The light exposure helps to regulate your circadian rhythm and boost your mood. Light therapy can be used in combination with other treatments for depressive symptoms, such as antidepressant medications

If you do not notice a lift in your mood after consistently undergoing light therapy for a couple of weeks, or your depressive symptoms are too difficult for you to manage, seek help from your doctor.

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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