ABSTRACT
Optical transducers are available for a wide variety of measurement applications. The basic elements have been available and used for many years in instruments such as polarimeters for stress determination, it is developments in the following areas that have led to the range and scope of optical measurement systems now available: lasers, fibre optics, optical materials, photodetectors, and signal processing. Incandescent lamps have an electrically heated filament within an evacuated glass or quartz envelope and are widely used for general illumination and projection systems. Discharge lamps produce light as a result of collisions between free electrons and gas in a sealed envelope. Light emitting diodes provide a range of high efficiency, low cost, low intensity, near monochromatic light sources with relatively narrow spectral bandwidths. Thermal photodetectors operate by monitoring the generation of heat in the detector by the incident radiation.
