Theories About How Light Affects Mood and Sleep

In 1984, a psychiatrist at NIMH, Norman Rosenthal, published a paper on the use of bright light therapy in patients with this disorder. Since then, a large number of well-designed studies have confirmed and refined these findings. Researchers are still investigating the mode by which bright light can lift depression or reset a sleep cycle. One theory is that an area of the brain, near the visual pathway, the suprachiasmatic nucleus, responds to light by sending out a signal to suppress the secretion of a hormone called melatonin. Brain studies suggest that there is impairment of the serotonin function in neurons leading to the suprachiasmatic nucleus.

Initial theories suggested a pathway from the retina to the suprachiasmatic nucleus. However some recent research indicated that bright light applied to the back of an individual's knee could shift human circadian rhythms. (Daily sleep-wake cycle) This suggests that the bloodstream, not just the neurons of the visual pathways, might mediate the biological clock.

How the Light Box is Used

Before embarking on a course of light treatment, it is best to have a complete psychiatric evaluation. Sometimes a medical illness or another psychiatric condition can masquerade as depression. Discuss various treatment alternatives with your doctor. Light therapy does take time, and regular use. Like exercise, not everyone who would benefit from it will actually do it on a regular basis. Your doctor will discuss the various types of light boxes or visors available. The time spent in front of the light is related to the intensity of the light source and the distance one sits from the light. The light devices cost about $250 to $500 and often are not covered by insurance. (Your doctor may lend out a box for a month so that the individual can see whether it helps before purchasing a box.)

Some individuals who use a 10,000-lux box may only need 30 minutes of daily light treatment. However, the amount of light needed varies widely from individual to individual. The light treatment is most often done in the morning, but studies have suggested that either morning or evening light can help SAD. Some people may get insomnia when they use the light in the evening. Initially, researchers felt that one needed full spectrum light. Now, studies suggest that regular fluorescent lights will work as well. UV (ultraviolet) light can damage eyes and skin, so it must be filtered out. It is best to buy a commercially built light box to be sure of the exact amount of light and to be sure that there are no isolated "hot spots" which could damage eyes. Many people still prefer full spectrum (minus UV) light because it is closest to natural lighting.

The individual measures the distance from her face to the light source. This measurement is important, and should be repeated daily for several days and occasionally after that. The light needs to strike one's eyes, but one does not need to look directly into the light source. It is fine to occasionally glance directly into the light. Many people read a book or eat breakfast while using the lights.

Sitting still for 30 minutes to several hours is not an option for some people. For these people, the light visor is an option. Others are able to take one of the compact light boxes to work and use it for several hours. It is best to use the light source in an uninterrupted time block, but it can be helpful even with some interruptions.

Long term treatment compliance is often more difficult than one might initially anticipate. This is an important reason to have a professional monitoring. Having to account for your regular use (or the lack thereof) is a powerful motivator. It is also helpful to have an outside objective individual to help monitor your response to the treatment.

Since one of the symptoms of SAD can be difficulty awakening in the morning, some find it helpful to have the light turn on just before they are supposed to wake up. Some individuals like to use a Dawn Simulator. This is a bright light that is programmed to gradually increase its intensity such that it reaches its full intensity a set period before the individual is scheduled to awaken. Although it is less gentle, some people will put their light box beside their bed and hook it up to a timer set to turn on shortly before awakening.

Some people like to use full spectrum light bulbs for everyday household use. There is no evidence that these low intensity bulbs affect mood or sleep phase. Your plant light will not cure your SAD. Your 10,000-lux light however, may be nice for some of your plants.

Other Uses of Bright Light Therapy

There has been research using light therapy for PMS, obesity and non-seasonal depression. The results have not been as striking as the results for SAD. More research needs to be done. However, it may make sense to use light therapy as an augmentation of other depression treatments or in cases in which the individual is unable to use other forms of treatment. The study on obesity was small and needs to be repeated with a larger, more carefully selected group. The obese individuals may have lost weight because their depression was better. Individuals whose PMS was worse in the winter responded better to light therapy than individuals with PMS without a seasonal variation.

continue: Additional Treatments for Seasonal Affective Disorder (SAD)