Optical sensors are available in four types. Direct Reflection: The emitter and receiver are located in the same housing. The detection of an object is obtained by the reflection of the inffared light off of the object. In the use of photocells it is important to note that the color and type of surface can effect the operating distance. The operating distance in the technical data is related to matt white paper. Reflection with Reflector: The emitter and receiver are located in the same housing. The reflection of the light emitted is obtained by using one or more reflectors and the detection of the object occurs when these rays are interrupted. This type offers a greater operating distance then the direct reflection type. Polarized Reflection with Reflector: Similar to reflection with reflector except that this type uses a polarized band of light. A polarized band of light offers a more secure readings even when the object has a very shiny surface and they are not affected by random reflections. Thru Beam: In this type the emitter and receiver are in separate housing and must face each other. Detection achieved when object interrupts the light beam between the emitter and receiver. This type offers the greatest operating distance. All models available with cables or conectors, are short circuit protected and compliant with the CE EMC directive.