What is Bright Light Therapy?

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  • Written By: Stacy Ruble
  • Edited By: Angela B.
  • Last Modified Date: 22 November 2019
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Bright light therapy, also called light therapy or phototherapy, involves exposing the patient to intense light, usually via a light box. The light box consists of 2,500- to 10,000-lux fluorescent bulbs with a diffusing screen. The intent is for the light box to mimic natural outdoor daylight. Bright light therapy is most commonly used to treat seasonal affective disorder, although it is also used to treat depression and sleep disorders.

Patients using a light box sit near the box, with their bodies oriented toward the box so they're not looking directly at it but the light is hitting their eyes. Bright light therapy is thought to be most effective when used during the pre-dawn and post-dusk hours of fall and winter when natural light is absent. Phototherapy sessions last between 15 minutes and two hours, with most patients having 30-minute sessions. During the bright light therapy sessions, patients simply conduct normal daily activities such as reading, eating or watching TV.

Bright light therapy is not intended to cure seasonal affective disorder or depression, but it may lessen the symptoms of these ailments. It is unclear why phototherapy works, but it is thought that replacing the early morning and late afternoon light adjusts the body’s internal clock. By shifting the clock, body mechanics such as temperature, sleep and hormones are affected. This physiological effect results in a therapeutic response, but the science on why requires further study.


There can be some side effects for bright light therapy box users. Some patients experience headaches, eyestrain or nausea during the first few sessions. If these effects continue, the bright light therapy sessions can be shortened, or the patient can move farther away from the light box. A more rare response to therapy is hyperactivity that makes the patient feel high, irritable, restless, manic and/or agitated.

Some people have conditions or circumstances that are contra-indicators for phototherapy. People who have eye problems, such as glaucoma, cataracts or retinal detachment, may not want to use a light box. People who are taking medications that warn against sunlight exposure will want to avoid phototherapy while on them. Even though light boxes are built to filter out harmful UV rays, people with a history of skin cancer or who have skin conditions making them sensitive to light should not engage in bright light therapy. Given the potential risk of harm, people are discouraged from building their own light boxes or from undergoing bright light therapy without medical advice.


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