Bright artificial light is best known as a treatment for winter depression or seasonal affective disorder. There have been a few small studies of light therapy for treating women with severe premenstrual symptoms. While some of the results are promising, more research is needed to learn how effective it really is. One study of 14 women that found light to be effective exposed them to 10,000 lux of cool-white fluorescent light for 30 minutes in the evening for the 2 weeks before the start of their periods. Light therapy is still considered experimental, and recommendations for the intensity, duration and timing of light exposure should be obtained from a professional trained in its use.