Define Essential Parts of Photocolorimeter - Light Source?

The light source is usually a tungsten lamp, for wavelength in the visible range (320-700 nm) and a deuterium or hydrogen lamp for ultraviolet light (below 350 nm). Hydrogen lamp is usually preferred to UV range. All the UV sources must be fitted with quartz or silica glass windows. Black body radiators are usually sources of infrared radiations the nernst glower being frequently used and this consists of to hollow rod made of fused oxides of zirconium, ytrium and thorium. Before use, it is preheated and when a voltage is applied, it emits intense continuous infrared radiation with very little visible radiation.