Depression Health Center

Key points

• Bright light therapy is an effective treatment for seasonal affective disorder (SAD).
• Light therapy is easy and safe. It has few side effects and can be done at home.
• People who have eye problems or take medicines that cause sensitivity to light should not use light therapy without first consulting a doctor.

Light therapy is treatment with a special type of light that is much brighter than a lamp or other light fixture in your home. The most common form of this therapy is done with a light box that contains fluorescent-not ultraviolet or full-spectrum- lights.

To use light therapy, you sit at a prescribed distance from the light box. The amount of exposure you need depends on the intensity of light you use and could range anywhere from 30 minutes to 2 hours. The intensity of light usually ranges between 2,500 and 10,000 lux (10,000 lux is about 20 times as bright as normal indoor lighting).

Although light boxes are the most common type of light therapy, dawn simulation is also used. With dawn simulation, a low-intensity light gradually comes on while you're sleeping, about 2 hours before you usually wake up.

Most people with seasonal affective disorder become depressed in the fall and winter, when days are shorter and sunlight is limited. Although researchers are still studying the exact cause of SAD, some believe the body's 24-hour biological clock (circadian rhythms), which controls sleep/wake cycles, may be affected by seasonal changes of light and darkness and that subsequent biochemical changes in the brain may cause depression. Light therapy helps to "reset" your biological clock.

Light therapy, which has few side effects, is also an alternative to taking medicines to treat depression. It can also be used with medicines and counseling.

Most light therapy is prescribed at 10,000 lux for about 30 minutes to 2 hours in the early morning. Studies vary as to whether light therapy at other times of the day is less effective. But some people with SAD (perhaps those who wake up normally in the early morning) should do their light therapy for 1 to 2 hours in the evening, ending 1 hour before bedtime.

Some people who find it inconvenient to use a light box may want to try dawn simulation.

When you begin light therapy, your first response will show you whether you need to adjust the intensity or duration. Many people respond to light therapy within 3 to 5 days. But they may relapse back into depression if they miss treatment for 3 days in a row during winter.¹ If you don't respond to treatment within the first week, you may notice improvement in the second week.

The most common side effects of light therapy include headache, eye strain, and nausea. You may be tired during the first week because of changes in your sleep/wake patterns, but this will usually go away after about a week.

Light therapy is usually started in the fall and continued through spring.

Your doctor can help you decide which light exposure schedule will work best for you. Most lights used in light therapy can be found on the Internet. Beware of manufacturers that market inexpensive light therapy devices that have not been researched for effectiveness or documented for safety. The safest light is fluorescent, not full-spectrum or ultraviolet light.

If you have any eye problems, talk with your ophthalmologist before beginning light therapy. Also, make sure your doctor knows all of the medicines you are taking.

Talk with your doctor

Take this information with you and work with your doctor to create a treatment plan that works for you.