section we are interested primarily in those light radiation and convert it into an electrical form.The general class of light-radiation transducers, also known as phototransducers, is used to detect the presence and inten sity of light under various circumstances. In fact, many photo-transducers can be made Jmuch more sensitive to light radiation than the human eye is The three primary types of light-to-electrical energy transducers are 1. Photoemissive devices 2. Photoconductive devices 3. Photovoltaic devices Each of these types possesses special advantages over the others.