Font Size

Seasonal Affective Disorder: Using Light Therapy

What is an Actionset?

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 who take medicines that cause sensitivity to light should not use light therapy without first consulting a doctor.

Return to topic:

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 lights (not full-spectrum or ultraviolet light). 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).

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. It could range from 30 minutes to 2 hours.

Most lights used in light therapy can be found on the Internet. Look for lights made specifically to treat seasonal affective disorder (SAD). Beware of manufacturers that market inexpensive light therapy devices that have not been researched for effectiveness or documented for safety.

Light boxes are the most common type of light therapy, but 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.

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

Test Your Knowledge

The amount of time I need to sit in front of a light box depends on how strong a light I use.


Most people who have seasonal affective disorder become depressed in the fall and winter, when days are shorter and sunlight is limited. Researchers are still studying the exact cause of SAD, but some believe lack of light may be the key. Seasonal changes in light may upset the body's 24-hour biological clock, which controls sleep-wake cycles and other circadian rhythms. Lack of light may also cause problems with serotonin, a brain chemical that affects mood. 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.

Test Your Knowledge

Professional counseling, medicine, or a combination of the two may still be needed even if I have light therapy.


Place the light box on a desk or table, and sit in front of it at the specified distance. You can do this while you read, eat breakfast, or work at a computer. The light should reach your eyes, but don't stare at the light box.

Light therapy is usually prescribed for 30 minutes to 2 hours a day, depending on the intensity of the light used and on whether you are starting out or have been using it for a while.

Most light therapy is prescribed at 10,000 lux to be used 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. Your doctor can help you decide which light exposure schedule will work best for you.

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

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. 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.

Test Your Knowledge

I should receive 10,000 lux of light therapy each morning for about 30 minutes to 2 hours every day.


Talk with your doctor

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

Other Works Consulted

  • American Psychiatric Association (2010). Practice Guideline for the Treatment of Patients With Major Depressive Disorder, 3rd ed. Available online:

ByHealthwise Staff
Primary Medical ReviewerKathleen Romito, MD - Family Medicine
Specialist Medical ReviewerAlfred Lewy, MD, PhD - Psychiatry
Last RevisedMarch 14, 2013

eMedicineHealth Medical Reference from Healthwise

This information does not replace the advice of a doctor. Healthwise disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.

To learn more visit

© 1995-2014 Healthwise, Incorporated. Healthwise, Healthwise for every health decision, and the Healthwise logo are trademarks of Healthwise, Incorporated.

Medical Dictionary