TRICARE South beneficiary enjoying sunlight on her face


Light Therapy

What is Light Therapy?

Light therapy (phototherapy) is exposure to a light brighter than indoor light but more closely mimics natural outdoor light. 

Who can benefit from Light Therapy?

Light therapy is one of the many ways to treat a variety of mental disorders and conditions affected by time changes or shift changes, especially Seasonal Affective Disorder (SAD) - a condition characterized by recurrent episodes of depression – usually in late fall and winter – alternating with periods of normal or high mood the rest of the year. 

Who should not use Light Therapy?

Patients should always check with their doctor before initiating light therapy- particularly if:
  • Patient’s skin is sensitive to light
  • Patient takes medications that react with sunlight, such as certain antibiotics or anti-inflammatories
  • Patient has an eye condition that makes their eyes vulnerable to light damage

Understanding SAD to understand Light Therapy

Hormones manufactured deep in the brain automatically trigger attitudinal changes at certain times of year. Experts believe that SAD is related to these hormonal changes. One theory is that reduced sunlight during fall and winter leads to reduced production of serotonin in the the brain. Serotonin is a neurotransmitter with a soothing, calming effect. The result of there not being enough serotonin is feelings of depression along with symptoms of fatigue, carbohydrate craving, and weight gain. Exposure to bright light from a light therapy box is thought to (1) alter your circadian rhythms (a name given to the "internal body clock" that regulates the 24-hour cycle of biological processes in animals and plants) and (2) suppress your body’s natural release of melatonin. These two results, in turn, can reduce depression symptoms particularly experienced in cases of Seasonal Affective Disorder. 

What kind of light is used in Light Therapy?

Bright white fluorescent light has been shown to reverse the winter depressive symptoms of SAD. Early studies used expensive "full-spectrum" bulbs, but these are not especially advantageous. Bulbs with color temperatures between 3000 and 6500 degrees Kelvin all have been shown to be effective. The lower color temperatures produce "softer" white light with less visual glare, while the higher color temperatures produce a "colder" skylight hue. The lamps are encased in a box with a diffusing lens, which also filters out ultraviolet radiation. The box sits on a tabletop, preferably on a stand that raises it to eye level and above. Such an arrangement further reduces glare sensations at high intensity, and preferentially illuminates the lower half of the retina, which is rich in photoreceptors that are thought to bring the antidepressant response. Studies show between 50% and 80% of users showing essentially complete remission of symptoms, although the treatment needs to continue throughout the difficult season in order to maintain this benefit.

There are three major dosing dimensions of light therapy, and optimum effect requires that the dose be individualized, just as for medications:
  1. Light intensity. The treatment uses an artificial equivalent of early morning full daylight (2500 to 10,000 lux), higher than projected by normal home light fixtures (50 to 300 lux). A light box should be capable of delivering 10,000 lux at eye level, which allows downward adjustments if necessary. 
  2. Light duration. Daily sessions of 20 to 60 minutes may be needed. Since light intensity and duration interact, longer sessions will be needed at lower intensities. At 10,000 lux – the current standard – 30-minute sessions are most typical. 
  3. Time of day of exposure. The antidepressant effect, many investigators think, is mediated by light’s action on the internal circadian rhythm clock. Most patients with winter depression benefit by resetting this clock earlier, which is achieved specifically with morning light exposure. Since different people have different clock phases (early types, neutral types, late types), the optimum time of light exposure can differ greatly. Long sleepers may need to wake up earlier for best effect, while short sleepers can maintain their habitual sleep-wake schedule.
Side effects of light therapy are uncommon. Some patients complain of irritability, eyestrain, headaches, or nausea. Those who have histories of hypomania (persistent and pervasive elevated or irritable mood) in spring or summer are at risk for switching states under light therapy, in which case the light dose needs to be reduced. There is no evidence for long-term adverse effects, however, and disturbances experienced during the first few exposures often disappear spontaneously. As an important precaution, patients with Bipolar I disorder – who are at risk for switching into full-blown manic episodes – need to be on a mood-stabilizing drug while using light therapy.
Sources:  Mayo ClinicNational Alliance on Mental Illness and Depression and Bipolar Support Alliance 

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Last Update: November 24, 2014