Bright light therapy

Bright light therapy means sitting near a special lamp, called a light box, for a set time each day. The light is much brighter than normal room light. It is best known as a treatment for depression that comes back every fall and winter, often called seasonal affective disorder (SAD).¹

Light therapy is simple, does not need a prescription, and has few side effects for most people. But it is a real treatment, not just a nice lamp. Timing matters, and some people need a doctor's advice before they start. This page explains what it can do, how it is used, and how to stay safe.

What light therapy is and how it may work

Light enters through your eyes, not your skin. A light box gives off bright white light, and good ones filter out ultraviolet (UV) light, the kind that can burn skin.¹ You do not stare into it. You sit near it with your eyes open while you read, eat breakfast or have coffee.³

Brightness is measured in lux. A 10,000 lux light box is about 20 times brighter than ordinary indoor lighting.¹

Scientists are still learning why SAD happens. Shorter winter days seem to lower serotonin (a brain chemical tied to mood). The body may also make too much melatonin (a hormone that makes you sleepy). Both chemicals help run your body's daily clock, so changes in them may throw that clock off.¹ Bright morning light is thought to help put this rhythm back on track.

Winter depression (seasonal affective disorder)

SAD is a type of depression that follows the seasons. In the most common form, symptoms start in late fall or early winter and go away in spring and summer.¹ About 5 in 100 U.S. adults have it. It is more common in women, in younger adults, and in places farther from the equator.²

Besides sad or empty mood, winter SAD often brings oversleeping, overeating, craving carbohydrates, and pulling away from people.¹ Read more on our page about types of depression.

What the research shows. Light therapy has been a main treatment for winter SAD since the 1980s.¹ A review for the American Psychiatric Association pooled controlled trials. People with SAD who used bright light were much more likely to get well (remission) than those given a fake treatment. Their odds of remission were almost 3 times higher.⁵ The 2023 Canadian (CANMAT) depression guideline still calls light therapy a first-line treatment on its own for winter depression, based on strong evidence.⁴

Not every expert body agrees on how strong the proof is. The U.K.'s National Health Service says there is not enough evidence for it to offer light boxes routinely, though many people find them helpful.⁷

Other proven choices for SAD. Light is not the only option:¹

Light therapy is for winter-pattern SAD. There is no specific treatment for the rarer summer pattern.¹

Depression that is not seasonal

Light therapy has also been studied in depression that lasts all year. The CANMAT guideline says recent reviews show it works, though results vary from study to study. Effects look larger when light is combined with an antidepressant.⁴

Based on this, the guideline lists light therapy as:⁴

• A second-line choice on its own for mild nonseasonal depression
• An add-on to medicine for moderate nonseasonal depression

For severe depression, it is not a replacement for standard care. See our overview of treatment for depression and when depression doesn't get better.

Bipolar depression: helpful, but only with care

People with bipolar disorder can also have deep depressions. Bright light may help, but it can rarely tip a person into mania (a period of very high energy, little sleep and risky behavior).³ That is why anyone with bipolar disorder should use light therapy only with their doctor's guidance.

In a small trial, 46 adults with bipolar depression kept taking their mood-stabilizing medicine. Half got bright white light at midday. Half got dim red light. After 4 to 6 weeks, about 2 in 3 people in the bright light group (68%) were in remission, compared with about 1 in 5 (22%) in the dim light group.⁶

No one in that trial became manic. But the light was given at midday, not first thing in the morning. Sessions started at 15 minutes and slowly grew to 60 minutes over about 4 weeks.⁶ The study was small, and the researchers advised a careful, step-by-step approach.⁶ Learn more about bipolar disorder.

How to use a light box

Always follow the instructions from your doctor and from the device maker. Here is what a common routine looks like for winter depression:

1. Talk with your doctor first if you have bipolar disorder or an eye disease, or take medicines that make you sensitive to light. An eye checkup before starting is a good idea.³
2. Choose a box made for this purpose. Look for one rated at 10,000 lux that filters out UV light.^1,7
3. Use it in the morning, soon after you wake up. A usual session is about 30 minutes.^1,4 Some routines range from 20 to 45 minutes.^1,2
4. Sit about 2 feet away with your eyes open. Do not look straight into the light.³ Brightness drops quickly as you move farther away, so distance matters.
5. Use it every day through the dark months. Many people start in early fall, before symptoms begin, and keep going until spring.^2,3
6. Track how you feel. Some people feel better in one to two weeks.² If you see no change after 3 to 4 weeks, tell your doctor.³ A simple mood diary can help.

Why timing matters. Light affects your body clock. Sleep doctors use light at different times of day to move a person's sleep earlier or later.⁸ Morning is the usual time for depression. Do not change to evening use unless your doctor or a sleep specialist suggests it.

Dawn simulators are lamps that slowly brighten your bedroom before you wake. A review found they helped SAD, but all of those studies came from a single research group, so the proof is thinner.⁵

Side effects and safety

Most people have mild side effects or none. The most common are eye strain and headache.³ These often ease if you sit a little farther away or shorten the session. Tell your doctor if they continue.

Do not try to get the same effect by looking at the sun. Never look straight at the sun. Long hours of direct sun on the skin also raise the risk of skin cancer.²

Light therapy in later life and dementia

Older adults. Many older people spend most of the day indoors, sometimes in dim rooms. The same safety rules apply, and the eye checkup matters more with age, since eye diseases become more common. If you take many medicines, ask your pharmacist whether any of them cause light sensitivity. See depression in later life.

Dementia and sleep. People living with dementia often have a scrambled body clock. They may doze all day and be awake at night. The American Academy of Sleep Medicine suggests light therapy for older adults with dementia who have this irregular sleep-wake pattern.⁸ It is a weak recommendation, which means the evidence is limited and the benefit is uncertain.⁸ Promising

Simple daylight steps are worth trying first. The Alzheimer's Association suggests spending time outside in daylight when possible, and keeping the home well lit in the evening. Dim light can create shadows that confuse a person with dementia.⁹ See sleep problems in dementia and sundowning.

Questions to ask your doctor

Is light therapy right for me?

• Do my symptoms fit seasonal depression, or something else?
• Should I use light alone, or with therapy or medicine?
• Do any of my health problems or medicines make light therapy unsafe?
• Do I need an eye exam first?

How should I use it?

• What time of day, and for how long?
• How far should I sit from the box?
• When should I start in the fall, and when can I stop?
• How long should I wait before deciding if it works?

What if it does not help?

• What should I try next?
• Could CBT, exercise or medicine be a better fit?
• Should I see a mental health specialist? Our guide on starting therapy can help.

Light therapy works best as part of a full plan. Steady sleep times, daily movement, time outdoors and staying in touch with people all support mood. See self-help for depression and healthy sleep habits.

Education only. This page is general information written from the sources listed. It is not medical, legal or financial advice and does not replace a doctor, therapist or lawyer who knows your situation. How we write and check pages.