An optical sensor converts light rays into an electronic signal, and measures the physical quantity of light. When light hits the sensor, the sensor trips an accompanying photoelectrical trigger. A measuring instrument takes the measurement of the electricity output, which increases or decreases depending on the intensity of light. Optical sensors can measure changes in light intensity from single or multiple light beams, working on either a single point or through a distribution of points in an array. Compared to other sensors, optical sensors deliver benefits such as greater sensitivity, freedom from electromagnetic interference, wide dynamic range and electrical isolation. They are compact and lightweight, and amenable to multiplexing. Optical sensors are available in many types, such as diffuse reflective sensors, reflection light sensors and through-beam sensors, basically differentiated by the position of the emitter, receiver and retro-reflector. A diffuse reflection sensor is installed only at a single point and detects objects by reflecting the light from the detected object. Through-beam sensors have the emitter and receiver in separate housings, each aimed directly at the other. Among the various sensors are several types, of different wavelength, switching intervals, range, output and power voltage. Effective installation of optical sensors may require accessories such as reflectors and mounting barriers.