LDR Full Form

LDR full form is Light Dependent Resistor. LDR is a special kind of resistor. Mathematically, the resistance of the LDR is calculated by the quantity of light which falls on the surface of the LDR. The working of LDR is completely dependent on the amount of light falling on the surface. There are two types of LDR namely Intrinsic Photoresistor and Extrinsic Photoresistor.

What is the Full Form of LDR?

LDR full form is Light Dependent Resistor. LDR is very similar to a potentiometer also known as potmeter or pot. In case of a potmeter, to change the resistance of the pot, the knob of the pot needs to be rotated. Whereas, in the case of LDR, the change of the resistance only depends on the amount and with what intensity the light is falling on its surface.

The resistance of the LDR is considerably in indirect proportion to the amount of light falling on its surface. It means that if the amount of light falling on the surface of the LDR is increased, then the resistance of the LDR will decrease and vice versa. LDR can be used in many objects such as projects and in various applications like dark detectors, Automatic Street Lights and Motor speed control.

How is LDR Made?

To make an LDR, a semiconductor with very high resistance is needed. However, there is no demarcated P-N junction. Since LDR is made of semiconductors like cadmium sulfide, it shows all the characteristics of a semiconductor. The various other semiconductors that are used to make LDR are cadmium selenide, lead selenide, indium antimonide, etc. To construct an LDR, the semiconductors are placed in a zigzag position. On both ends of the semiconductors, metal contacts are put which helps in making a connection with the LDRs. A coating of transparent materials is done for the protection of these semiconductors, which is a photosensitive material. Moreover, the transparent coating is done to protect the LDR and the coating allows light to pass through and helps in the overall functioning of the LDR.

Working of the LDR

As per the estimation in physics, the working of the LDR is based on the ‘principle of photoconductivity’. When the light falls on the surface of the LDR, the energy of the light is absorbed by it. As LDR is made up of photoconductive material and because of the energy of the absorbed light, the electrons present in the valence band of the photoconductive material get charged and jump into the covalent band as a reaction. As a consequence of this, the conductivity of the LDR is increased. Therefore, this increased conductivity effect is the consequence of an increase in the amount of light that falls on the surface of the LDR.

In the practical application, for the working of the LDR, it is immensely needed that the energy is completely absorbed because the falling of light is larger than the bandgap energy so that the electrons present in the Valence band can get charged to reach the conduction band.

The resistance of the LDR reaches maximum when it is dark and in current it is calculated around 1012 ohms. Also, as the intensity of the light increases, the resistance of it decreases. The intensity of the light is inversely proportional to the resistance. Supposedly, if we draw the resistance and the intensity known as illumination of the light on a graph, then it will be a hyperbolic curve in nature.

Different Types of LDRs

There are different types of LDR which are responsible for different functions. Two basic type of LDR are:

1. Intrinsic Photoresistor

Intrinsic Photoresistors also known as a Photocell is a light-dependent resistor which is also called photo-conductive cell LDR are made using only pure semiconductors only and no doping is done while making them. The semiconductors which are generally used while making this kind of LDR are Germanium and Silicon. However, the working of these kinds of LDR is similar to other LDRs. In the process of working, when the high intensity light falls on the surface of the Intrinsic Photoresistor, some of the electrons from the valence band get charged up and jump to the conduction band.

2. Extrinsic Photoresistor

In making an intrinsic photoresistor, no pure semiconductors are used. Which literally means that semiconductors are used with the presence of some impurities like phosphorus while making it. Generally, this kind of extrinsic photoresistor is made for light which has long wavelengths.

Testing Process of LDR 

• For the testing of LDR, a multimeter is required for the testing of LDR which should be set up properly.
• The two sections of the LDR are connected with the multimeter's positive and negative terminals respectively.
• After the wires are connected with the right terminals, the light is put on the surface of the LDR. By using a torch to put light, it can be done. The meter is checked for the reading after this.
• Soon after the reading is checked in light, the meter reading is noted by putting the LDR in the dark.
• The difference in the resistance of the LDR can be seen in both scenarios (in light and darkness). It is observed that the resistance of the LDR in the dark can be seen high as compared to the resistance of LDR in light.