Seasonal affective disorder is a type of depression that affects some individuals during the winter months when there is less sunlight. One hypothesis is that since there are fewer hours of daylight during the winter months, the production of melatonin is affected, resulting in physical ailments such as drowsiness and lethargy. Additional symptoms of SAD include a craving for carbohydrates, increased appetite, weight gain, and mood swings. Many researchers believe light therapy is an effective treatment for SAD. Light therapy, also called phototherapy, involves sitting near a specially designed light box that produces a strong light. Most light boxes emit a light of 2,500 to 10,000 lux, which is between the average living room lighting of 100 lux and a bright sunny day of about 100,000 lux.