Deuterium or hydrogen lamps are used as radiasources capable of producing light in the range 160-375nm for UV radiation.
Other radiation sources for UV are Tungsten, lamp, xenon discharge lamp and mercury arc lamp. Sources for visible radiation are Tungsten lamp, mercury vapour lamp and carbonate lamp. However tungsten filament provides light from 320-2500nm for visible region. Radiation from the source enters the monochromator through the slit. The radiation is collimated and then strikes the diffraction grating or prism which split the beam into its
component wavelengths. By rotating a chopper light of a particular wave leaves the monochromator and is directed towards the sample cell/container. The container holding the sample is also called the cell. The cell should be transparent to the region of wavelength of measurement. Rectangular curettes made of quarts are used which are transparent in the 350-2000nm and 1cm thick. Radiation emerging from both the sample and reference cells are detected using photosensitive detectors such as photovoltaic cell, photomultiplier tube or photoemissive tube.
Intensity of light incident on a sample is denoted as Io while the intensity of light passing through the sample is I. The ratio I/Iois called the transmittance T. Transmittance is usually expressed as percentage transmittance (%T). Absorbance is related to transmittance:
A = -log (%T/100%)