Light Dependent Resistor (LDR) also referred to as photoresistor are simple and low-cost Sensors. It’ is also called a photoresistor or a photoconductor. It basically works on the principle of Photoconductivity. A photoresistor may be a passive component that decreases resistance with reference to receiving luminosity (light) on the component’s sensitive surface. The resistance of a photoresistor decreases with an increase in incident light intensity; in other words, it exhibits photoconductivity. This LDR are available in 5mm, 8mm, 12mm, and 25mm dimensions made from a high resistance semiconductor cadmium sulphide.
LDR made with a light-sensitive material placed on an insulating substrate like ceramic. The material placed in a zigzag shape so as to provide the specified power rating and resistance. It’s designed in such a way to provide the maximum possible contact area with the 2 metal films. Where the Ohmic contacts made on either edge of the leads. The structure protected using a clear plastic or resin case, to supply free access to external light. In the absence of light, designed to possess a high resistance within the range of megaohms. As soon as light falls on the sensor, the electrons liberated, and therefore the conductivity of the material increases.
When the light intensity exceeds a particular frequency, the photons absorbed by the semiconductor give band electrons enough energy to jump into the conduction band. This causes the free electrons or holes to conduct electricity and thus lowering the resistance. (< 1 Kilo ohm). These devices are used where there’s a requirement to sense the presence and absence of light is important. This module provides a wide range of applications in-camera light meters, street lights, clock radios, light beam alarms, reflective smoke alarms, and outdoor clocks. etc