One of the most frequently investigated hypothesis of the pathophysiology underlying Seasonal Affective Disorder(SAD) or so called winterdepression is a disturbance of circadian rhythms. Since the circadian system is especially sensitive for the blue portion of the light spectrum, a new light therapy device with more blue light (blue enriched polychromatic light) was tested for its efficacy to treat SAD. In chronobiological terms this light is hypothesized to be more potent in inducing non-visual effects. In the present study fluorescent tubes that emit a high portion of short wavelength light on top of the normal wavelengths are tested for its superiority in treating SAD. This blue-enriched light (colour temperature 17000 ºK) is compared to standard light treatment (5000 º K) in SAD patients., The investigators hypothesise that blue- enriched light improve the therapeutic effects of light treatment leading to a higher response or the same response in a shorter time schedule compared to standard light treatment.