Light Dependent Resistor Real-life example   Security System Controlled by An Electronic Eye This security system controlled by an electronic eye project is based on photo sensing arrangement. The proposed system uses a 14-stage ripple carry binary counter to sense the intensity of light using LDR. The o/p makes a relay and buzzer for the required action. This project is very useful to deter burglars from malls, banks and shops. This project or systems  uses a light dependent resistor. When light falls on the LDR sensor, then the resistance of the sensor decreases, which lead to activate an alarm to give an alert to the user. This project is suitable in the application of providing security system for different types of area or place  like lockers, cash boxes,  malls, shops. The circuit of this project is placed inside of the cash box in malls or inside of the lockers  in such a way that, when a burglar opens the cash box or locker and uses a torch light to search the valuables. When t

  Light Dependent Resistor (LDR)  Working Principle of Light Dependent Resistor (LDR) Light Dependent Resistor work based off of the principle of photoconductivity. Photoconductivity is an optical phenomenon in which the material’s conductivity is increased when light is absorbed by the material. When light falls i.e. when the photons fall on the device, the electrons in the valence band of the semiconductor material are excited to the conduction band. These photons in the incident light should have energy greater than the bandgap of the semiconductor material to make the electrons jump from the valence band to the conduction band. Hence when light having enough energy strikes on the device, more and more electrons are excited to the conduction band which results in a large number of charge carriers. The result of this process is more and more current starts flowing through the device when the circuit is closed and hence it is said that the resistance of the device has been decreased. 

  Light Dependent Resistor (LDR)  What is a Light Dependent Resistor (LDR) ? A Light Dependent Resistor is also known as a photoresistor or LDR. Light Dependent Resistor are also called as photoconductors, photoconductive cells or simply photocells. Light Dependent Resistor is a device whose resistivity is a function of the incident electromagnetic radiation. Hence, Light Dependent Resistor are light-sensitive devices.  They are made up of semiconductor materials that have high resistance. There are many different symbols used to indicate a photoresistor or LDR, one of the most commonly used symbol is shown in the figure. The arrow indicates light falling on it.