The most important components of an optoelectronic switch are the glass prism and an LED light source. Inside the glass prism there is a transmitter, a receiver and an infrared light. The light from the LED is shone into the glass prism, causing infrared light to reach the receiver. So long as the tip does not come into contact with the liquid to be measured, the light is reflected within the prism to the receiver. However, if the liquid in the container rises and envelops the tip of the optoelectronic switch, the light is refracted by the glass prism into the liquid and no longer reaches the receiver, or only very weakly. The switch then outputs this change as a modified switching signal and the LED display lights up. If the liquid in the vessel then drops again and the glass prism is no longer covered by liquid, the infrared light is also able to reach the receiver again and the LED display goes out. Learn more about how optoelectronic sensors work in our video “WIKA - Level monitoring with optoelectronic switches” .