UV-C lamps designated UVI are doped with a special amalgam which reduces the internal pressure of the mercury vapour. The amalgam means the lamp will give more than twice the power per unit of length produced by a conventional low pressure lamp. UVI lamps emit radiation mainly of the wavelength 253.7 nm but also 184.9 nm is possible. Therefore three different types of quartz are possible on customer request according to the intended application. Just like conventional low-pressure lamps, amalgam lamps are suitable for use in both air and water. However, the higher operating temperature of the latter must be taken into account in their application. They enable very compact, high-performance equipment to be designed. The fact that they can be used in water at quite high temperatures makes them very popular.