Red = 660nm Best choice for use with plastic fiberoptic light guides. Useful when sensing translucent objects in proximity (Beam Make) mode. Useful when sensing transparent objects in fiberoptic retroreflective (Beam Break) mode. Can be polarized for retroreflective (Beam Break) sensing to reduce proxing on shiny objects. Opposed fiberoptic light guides can be polarized for sensing some translucent plastic containers; consult factory for details. Used as red filter for color perception advantages.