Attenuator, Light

(or light weakener), an optical device designed to attenuate a light flux or, in the general case, a radiation flux. Light attenuators are made in the form of grids, iris diaphragms, scattering plates, rotating notched disks, interference light filters, photometer wedges, and solid, liquid, or gaseous light absorbing filters. Those that do not change the relative spectral distribution of the transmitted light are said to be neutral (nonselective); otherwise, they are called selective. The latter are used to alter the spectral composition or chromaticity of the radiation; in particular, they are used to select broad or narrow spectral bands or to eliminate spectral bands from transmitted light, or less often, from reflected light.

Light attenuators are widely used in photometry and spectrometry, for example, to equalize the intensities of light beams or to change the spectral sensitivity of detectors. They also have practical uses in such fields as printing and motion-picture technology.