Retro-reflective is the second most popular sensing method. This sensing method detects the presence of a target based on how much light is returned to the sensor after reflecting off a reflector. Similar to through-beam, this is a two-part setup, and they must be aligned so that once an object comes in front of the sensor, it has blocked the light from hitting the receiving element. A retro-reflective sensor requires the use of a reflector that is also properly aligned in order to sense. Depending on the reflector used, the E3Z Retro-reflective sensor can sense up to four meters. Clear object detection is a major application for these sensors because the light must pass through the object twice, causing more light to diminish, therefore, it can be detected by the receiving element. The E3Z’s retro-reflective sensors are also great for presence/absence at midranges where space or power supply constraints exist for which a through-beam cannot be used.