A basic slotted switch consists of an emitter on one side of an air gap and a sensor on the other. Most OPTEK slotted switches have emitters in the near-infrared wave lengths (890nm or 935nm). If a special wavelength is necessary, OPTEK can provide the emitter and sensor pair that meet the requirements.  Slotted switch housings are either opaque or transmissive to near infrared wavelength. Housings made with opaque material require an aperture (hole) for the light to go through. Transmissive housings are manufactured using a material that is clear to the appropriate near infrared wavelength. These devices may have apertures similar to the opaque devices and are used in areas with minimal ambient light. Transmissive devices can also be used in semi dusty environments.