Phototherapy involves subjecting the skin to waves of ultraviolet light. There are three types of ultraviolet light, UVA, UVB and UVC. There are treatments available using UVB light, lasers or UVA light combined with a medication called Psoralen (PUVA).
Conventional "Broadband" UVB lamps emit light in a broad spectrum that includes both the therapeutic wavelengths specific to the treatment of skin diseases plus the shorter wavelengths which can result for sunburn. Sunburn has a negative therapeutic benefit, increases the risk of skin cancer, and limits the amount of therapeutic UVB that can be taken. "Narrowband" UVB lamps, on the other hand, emit light over a very short range of wavelengths concentrated primarily in the therapeutic range. UVB Narrowband is therefore safer and more effective than conventional UVB Broadband.