Ultraviolet Phototherapy lights slow abnormal growth of normal skin cells. This light occurs naturally as a component of sunlight and is part of the ultraviolet light spectrum. Ultraviolet phototherapy uses different wavelengths of the UV spectrum based on which condition is to be treated. Ultraviolet phototherapy lights are the fastest, most effective, and safest treatment possible and has been shown to be very effective in treating psoriasis and in the repigmentation process for vitiligo.