Nowadays the preferred radiotherapy treatment of skin diseases like psoriasis is through the use of the ‘B’ bandwidth of the UV spectrum (290 to 315 nm), since this requires no photo-sensitizing agent. But some patients do not respond to UVB treatment, hence a UV lamp with an ‘A’ bandwidth of the UV spectrum is used, and here Philips offers a choice of either TL or PLS/PLL lamps. Both are ideal for when the UVB is unsuitable. These (PUVA) lamps have a wavelength of between 315 to 380 nm and are not only used for the treatment of psoriasis but are also commonly used for more than 20 other diseases.