The excimer laser is similar in principle to treatment with narrow band UVB, but delivers a single wavelength of light in the same way as lasers do. The wavelength of light emitted by Excimer laser is within the UVB range at precisely 308nm. This appears to be the most favourable wavelength to treat vitiligo. The light emitted is highly concentrated and hence more powerful than that associated with traditional narrow band UVB. As a result, the response times are much quicker (weeks rather than months). A negative of Excimer laser treatment however is that the area that can be treated is small, usually a maximum of 25 square centimetres.