The full form of LDR is Light Dependent Resistor. An LDR is a type of resistor. The amount of light that falls on the surface of the LDR is used to calculate its resistance. A potentiometer (potmeter or pot) is quite similar to an LDR. To adjust the resistance of the pot, turn the knob, however, in the case of LDR, the resistance simply changes depending on the amount and intensity of light falling on its surface.
The resistance of the LDR is proportional to the amount of light falling on its surface, which implies that as the amount of light falling on the LDR’s surface increases, so does the resistance of the LDR, and vice versa. LDR can be utilised in a variety of projects and applications, including automatic street lights, dark detectors, and motor speed control.
How is LDR Made?
A semiconductor with a very high resistance is utilised to create an LDR. There is, however, no P-N intersection.
Because it is built of semiconductors such as cadmium sulphide, LDR exhibits all of the characteristics of a semiconductor. Other semiconductors utilised in the production of LDRs include indium antimonide, cadmium selenide, lead selenide, and others.
To create an LDR, semiconductors are held in a zigzag pattern. Metal contacts are placed on both ends of the semiconductors to aid in the connection with the LDRs.
A transparent material coating is used to protect these semiconductors, i.e. photosensitive material. Furthermore, the clear coating used to shield the LDR allows light to pass through, which aids in the overall operation of the LDR.
How Does LDR Work?
The LDR operates on the basis of the photoconductivity concept. When light falls on the surface of the LDR, the energy of the light is absorbed by it because the LDR is made of photoconductive material, and the electrons present in the valence band of the photoconductive material become excited and jump into the covalent band, increasing the conductivity of the LDR. This impact is caused by an increase in the amount of light that falls on the LDR’s surface.
It is critical for the LDR to absorb energy because the falling light is greater than the bandgap energy, allowing electrons in the Valence band to be energised and move into the conduction band.
When it is dark, the resistance of the LDR reaches its maximum and is calculated to be roughly 1012 ohms. Also, as the intensity of the light grows, its resistance diminishes. If we plot the resistance and intensity (illumination) of light on a graph, it will be hyperbolic.
Also Read: What is the Full Form of IPC?