These sensors were developed early in my career. They were used in web guiding systems to control the lateral registration of materials processed in continuous sheet form. The reflex edge sensor was used for edge sensing in the metals industry. The light source was a high intensity sealed reflector lamp. A retroflector strip (like the ones used for highway markers) returned the light beam to the sensor from as far as eight feet away. A beam splitter directed part of the returning light to a photosensor. Polarizing filters and internal baffles reduced the effect of unwanted reflections.  The high performance line/edge sensor was used in the packaging industry and could sense printed markings made with opaque or transparent ink on a variety of substrates ranging from matte textured paper to highly reflective foil. It relied on high quality optics and a polarizing filter that could be set by the operator to take maximum advantage of differences in the way metal and dielectric surfaces reflect polarized light. The low cost line/edge sensor was used to sense lines or edges in situations where contrast was consistently high.