Most people with winter-onset SAD can benefit from light therapy, but in light therapy, the devil is in the details. A very basic, bottom line description of light therapy is that it consists of light entering the patient's retina from a prescribed distance for a prescribed amount of time. But distance and angle of the light, time of day the therapy is performed and amount of light need to be taken into account, tested and possibly tweaked to get the best result for each patient.
Intensity of light
A standard light box will emit 10,000 lux of fluorescent light (lux is the standard of measurement for the intensity of light that a natural or artificial light source emits). For Seasonal Affective Disorder, the therapeutic range falls between 2,500 and 10,000 lux. It will take some experimentation to find the right range for you. Using a light box in the higher range usually translates into a shorter session time.
Time of day
Time of day is important. Most people will get the best results from light therapy if it takes place in the early morning. One study looked at how light therapy conducted at different times of the day and different lux strengths caused the remission rates among the study subjects to vary. The study found that the rate of remission in subjects using light therapy in the morning was significantly higher than that of subjects undergoing light therapy in the evening.
Length of exposure
Length of exposure for successful light therapy varies from person to person. For most people, the range is between twenty and ninety minutes per day. Your doctor may recommend starting somewhere in the middle and experimenting until you feel that you have found the amount of time that relieves your symptoms.
Location and positioning of box
You should set the light box up wherever you will be able to receive the optimum exposure for the entire length of time. For some people this means sitting next to the light and reading, watching tv or doing another type of fairly stationery activity. You may need to experiment a bit to discover the optimal distance for you, but you should start at the typical range of 2 feet.
If possible, position the light box toward the eyes at an angle. If the light source is tilted forward, more light is able to enter the eyes. Positioning at an angle also decreases the glare and the light box is more comfortable to use. Positioning the box upright instead of at an angle, however, will project light further into a room.
Some light boxes give you both options. As with other aspects of light therapy, the option you go with may depend on what type of light box you can afford and where you set up your box.
As you can see, the number of possible variations in time of day, length of exposure, angle of light and combinations thereof can make finding the exact recipe for your optimal light therapy somewhat challenging. If possible, you should undertake a course of light therapy under the guidance of a psychiatrist, preferably one with some experience in directing patients in light therapy.