Nowadays the preferred radiotherapy treatment of skin diseases like psoriasis is through the use of the ‘B’ bandwidth of the UV spectrum, 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 a TL or the more compact PLS/PLL lamps. Both are ideal for when the ‘B’ bandwidth of the UV spectrum is ineffective. 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.