Our health, mood, and behavior are affected when the quality and quantity of sunlight is lessened. Today's modern, urban lifestyles often keep us indoors, away from daylight. In addition, shorter winter days, cloudy skies, shift work and jet travel can affect our circadian rhythms adversely.

Seasonal Affective Disorder (SAD) is a form of seasonal clinical depression. It generally starts each year between September and January, and disappears during the longer days of April or May.

During the winter, people with SAD are likely to experience fatigue, sadness, difficulty concentrating, increased sleep (though without feeling rested), carbohydrate craving and weight gain, feelings of being overwhelmed, loss of libido and irritability. People suffering from SAD may experience these and other symptoms to such a degree that they are unable to function normally, and often feel chronically depressed. SAD affects about 11 million North Americans.

The Winter Blues or (SubSAD) is a milder form of seasonal depression but can still cause distress and severely limit one's day-to-day activities. Winter Blues may affect an additional two to three times as many people as SAD does, or up to 25% of the population in northern latitudes.

Bright light therapy has been researched and implemented in the United States and abroad since 1981. It involves exposure to intense levels of light that replace the light normally found in sunlight.

As light enters the eye, it hits the retina and is transmitted by nerve impulses to the pineal gland. The pineal gland controls melatonin and serotonin secretions. These set the body's internal clock or circadian rhythm.

Light therapy can raise the level of serotonin in the day and melatonin at night. Serotonin keeps us alert and full of energy during the day while melatonin helps us rest and recuperate at night. Both promote optimum health. Light therapy helps to adjust the body's melatonin timing so that it receives the same amount that it produces during the winter as in summer.

Melatonin has been shown to counteract stress, boost the immune system to help fight off viruses and bacteria, improve the quality of sleep, minimize jet lag, reduce the risk of heart disease and regulate biological rhythms. Melatonin may also protect against cancer and play a role in determining how long we live.

Bright light therapy consists of sitting close to a light box with eyes open so that the light shines on the user's face. Looking directly at the light is not necessary. One is free to read, write or eat a meal while staying oriented towards the light. This can also be a pleasant time to meditate or listen to music.

Sitting within the 10,000-lux range of a light box for a 30-minute session soon after awakening is a typical treatment. This equals sitting in the 2,500-lux range (about double the distance, but 1/4th the light intensity of the 10,000 lux range) for a 2-hour session. Moving towards or away from the light changes intensity levels.

Light box brightness levels can vary between manufacturers, so check to find the particular 10,000 lux range of your light box. The 10,000 lux range is about 2 feet for the North Star 10,000. As a measure of comparison, note that 100 lux is the amount of light entering one's eyes from a 100-watt bulb five feet away.

Once adjusted to light therapy, an individual gets a fairly good intuitive feel for the results and soon learns to adjust the session length to achieve optimum results. Treatment time can range from between 15 minutes to three hours in the 10,000 lux range.

A positive response usually begins within two to four days after beginning light therapy, but it could take up to several weeks to get the full beneficial effect. After the first week of accustoming oneself to light therapy, it is fine to spend more time with it. This is especially helpful on cloudy days, or for those who have an office without a window. A light box can be like a window of sunshine!

Some people can skip treatments for one to three days, occasionally longer, without ill effects, but most have symptoms returning quickly when treatment is interrupted. Bright light therapy helps with SAD, SubSAD, sleep disorders, PMS, jet lag, and shift work adjustment. Many insurance companies will reimburse the purchase of a light box when a doctor or therapist prescribes light therapy.

This information is intended to provide readers with general information about the current use of light therapies. No medical instructions or advice is intended. It is suggested that all interested persons seek the advice of a skilled clinician.