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. 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.