By Mayo Clinic staff

In the depths of winter, you may turn your face to the afternoon sun, seeking out what little light filters through fading gray skies. You may throw open the blinds, leave lights on throughout your home, or even head South for a vacation — anything for a little more light.

For people with a type of depression called seasonal affective disorder, this need for light takes on greater significance. Light may be instrumental in treating potentially debilitating symptoms of the disorder.

Hope through light therapy

People with seasonal affective disorder have a cyclical type of depression that's most often triggered by the onset of fall or winter, when daylight hours wane. In rare cases, the condition develops during summer months. Signs and symptoms of winter-time seasonal affective disorder can include sadness, sleep difficulties, increased appetite, carbohydrate craving, irritability, weight gain, lack of energy, anxiety and problems concentrating. Symptoms can be severe enough to interfere with your daily activities and quality of life for months on end. You may find your symptoms gradually abating with the arrival of spring, and sunnier, longer days.

But what can you do in the meantime, during those dark days when you can't get out of bed, when you skip work, miss deadlines, overeat, or feel overwhelmed by fatigue or despair? Because symptoms can be severe, don't try to ride them out or treat them yourself. Consult your doctor or a mental health professional for help.

There's a good chance that therapy with specialized lights — not your ordinary living room lamp — will help reduce your symptoms and enable you to enjoy life more again.

Light therapy, also called phototherapy, has been used to treat seasonal affective disorder since the early 1980s, and it has many benefits. It's easy to use in your own home, it usually doesn't have major side effects, it's generally safe, and it's cost-effective. In fact, light therapy is now considered standard treatment for seasonal affective disorder.

How it works

Light therapy is typically administered using a light box. Light boxes are made up of a set of fluorescent bulbs or tubes generally encased in small, portable devices of plastic or aluminum. The bulbs are covered with a plastic screen that helps block out potentially harmful ultraviolet (UV) rays that can cause cataracts and skin problems.

The light box can be set on a table or desk, right in your own home or your office. You sit in front of the light box with your eyes open. In order to work, the light from the box must enter your eyes indirectly; skin exposure isn't effective. Don't look directly at the light box because the light can damage your eyes.

Why it works

Researchers are still trying to pinpoint precisely what causes seasonal affective disorder. Some evidence suggests that the disorder arises from abnormalities in how the body manages its internal biological rhythms or matches those rhythms to the 24-hour day. Genetic factors may also be involved. The balance of evidence favors the idea that changes in the light part of the day-night cycle induce biochemical changes that bring on seasonal affective disorder.

While several biochemical alterations have been noted, evidence shows that the hormone melatonin plays a big role. Melatonin helps control your body's internal (circadian) rhythms of body temperature, hormone secretion and sleep. It's produced in a specific area of your brain during darkness.

During the low-light months of autumn and winter, people with seasonal affective disorder produce more melatonin — enough to cause potentially debilitating symptoms of depression. But exposure to bright light can suppress the brain's production of melatonin, helping regulate your body's internal clock and reducing those symptoms.

Researchers also speculate that light therapy causes changes in neurotransmitter activity in certain brain areas. Scientists are studying the effects of bright light on production of the neurotransmitters serotonin and dopamine, two chemicals that also have a role in depression.

Simply sitting in front of a lamp in your living room at home won't relieve symptoms of seasonal affective disorder. Indoor lights don't provide the type or intensity of light that's necessary to treat the condition. The specialized light boxes used for seasonal affective disorder emit light that's comparable to outdoor light just after sunrise or just before sunset.

Keys to success

There are three keys to effective light therapy:

Intensity. To work well, the light you receive must have the right intensity. Light box intensity is recorded in lux, which is a measure of the amount of light you receive at a specific distance from a light source. Light boxes for light therapy usually produce between 2,500 lux and 10,000 lux. Typical therapy is at 10,000 lux. In contrast, the lighting in an average living room in the evening is less than 100 lux, while a bright sunny day may register 100,000 lux.
Duration. Therapy typically involves daily sessions ranging from 15 minutes to two hours. When you start treatment, your doctor may advise therapy in smaller blocks of time, working up to longer periods.
Timing. For most people, light therapy is best used in the morning, after you first wake up. There's a short period of time after waking when your body clock can essentially be turned back by light therapy. In addition, using light boxes at night can make it difficult to sleep.
The most effective combination of intensity, duration and timing varies from person to person, so you may have to adjust your routine to find what works best. Your doctor can guide you about how to make appropriate adjustments for your situation.

An effective treatment

With appropriate light therapy, you may start to feel better in just two to five days. In some cases, though, it can take several weeks. Adhering to a consistent daily routine can help ensure that you maintain those benefits over time.

The general recommendation for most people with seasonal affective disorder is to begin treatment with light therapy in the early fall, as soon as the first symptoms start. Treatment generally continues until spring, when outdoor light alone is sufficient to sustain a good mood and higher energy.

Light therapy does require a time commitment. Some people quit because they don't want to spend a lot of time sitting by a light box. But light therapy doesn't have to be boring. You can read, use a computer, write, watch television, talk on the phone or eat breakfast while undergoing light therapy. You may also be able to use a light box at work. Before giving up, talk to your doctor about fitting light therapy into your daily routine. If you interrupt light therapy during the winter months or stop too soon in the spring when you think you're improving, your symptoms may return quickly.

Side effects from light therapy are uncommon. Some people experience eyestrain, headache, agitation or insomnia. You can usually manage these problems by changing the length or timing of your light box treatments — problems are more likely to occur with evening treatment.

A word of caution: Light therapy may not be right for you if your skin is sensitive to light. Light boxes could pose a risk if you have light-sensitive skin, if you take medications that react with sunlight — such as certain antibiotics or anti-inflammatories — or if you have an eye condition that make your eyes vulnerable to light damage. Even though light boxes are widely available in the marketplace without a prescription, check with your doctor before using a light box to avoid the dangers.

Sometimes light therapy alone isn't enough to effectively treat seasonal affective disorder. If your symptoms haven't decreased within a few weeks, talk to your doctor. An antidepressant or psychotherapy may help. In addition, researchers are studying new devices called dawn simulators that may be used with or instead of light therapy. Dawn simulators provide a low-intensity light while you sleep, gradually increasing in illumination until you wake.

Light therapy may be helpful in conditions other than seasonal affective disorder. Some research shows that it may also help relieve symptoms of obsessive-compulsive disorder, such as rechecking door locks numerous times and repeatedly turning water taps off and on. And it may be useful if you have depression and are pregnant, since some antidepressants may be harmful to the developing fetus.

Light box features

Commercial markets offer a wide variety of light boxes and other light devices used in light therapy. You can buy them on the Internet and at some drugstores and hardware stores. But not all of these products are effective or safe, so check with your doctor before buying one. And to avoid complications, use the device only under your doctor's guidance.

Here are some considerations when buying a light therapy box:

Intensity. Look for a light box that allows you the right intensity at a comfortable seating distance. Some light boxes offer 10,000 lux only when you're within a few inches of the box, while others can reach a distance of nearly two feet.
Minimal UV exposure. Some light devices use full-spectrum light bulbs that give off UV light, which can cause eye and skin damage. Look for devices that produce as little UV light as possible at high intensity or that carefully shield the UV rays they produce.
Light direction. Light should come from above your line of sight, not at it or below it, so make sure you can position the light box appropriately.
Blue light. Exposure to the blue light spectrum should be minimal, since it can create glare or visual difficulties.
Cost. Prices vary greatly, from $100 to several hundred dollars. Check with your insurance company to see if your benefits will cover the cost.
Style. Some light boxes look like upright lamps, while others are small and rectangular. One design that hasn't yet been proved effective resembles a visor and is worn on your head. Look for a light box with the features you need and that you find attractive.
Convenience. Some light boxes are bigger than others, which can make them less portable. Find one that you can move around easily and that fits the desired location in your home or office.

A brighter future

Light therapy offers a chance to regain the happier mood and brighter outlook you lose to seasonal affective disorder. Although it's generally safe and effective, don't try to treat yourself, or you may risk eye or skin damage. With appropriate light therapy, you may no longer have to endure a seasonal descent into darkness.

April 09, 2004
MH00023

© 1998-2004 Mayo Foundation for Medical Education and Research (MFMER). All rights reserved. A single copy of these materials may be reprinted for noncommercial personal use only. "Mayo," "Mayo Clinic," "MayoClinic.com," "Mayo Clinic Health Information," "Reliable information for a healthier life" and the triple-shield Mayo logo are trademarks of Mayo Foundation for Medical Education and Research.

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