What is LDR? (Photoresistor) – Types, Working, Application, Diagram & Symbol [Complete Details]

What is LDR?

What is LDR? Types, Working, Application, Diagram & Symbol [Complete Details] :- Its full form is Light Dependent Resistor or Photoresistor, which is a passive electronic component. Usually, it is a resistor whose resistance changes with the change in light intensity. A photo resistor is consists of a high resistance semiconductor that absorbs photons. Based on the number and frequency of the absorbed photons, the semiconductor material delivers electrons satisfactory energy to fall into the conduction band.

The resulting free electrons carry electricity succeeding in decreasing the resistance of the photo resistor. The quantity of electrons is directly proportional to the frequency of the photon.

LDR Symbol

Types of Photoresistor ( LDR )

Photo resistors (LDRs) can be classified into two types depending on the materials used to build them. The two types of photo resistors include:

1. Intrinsic Photoresistor: ( Types of LDR )

These are made up of pure semiconductor materials such as silicon or germanium. Electrons get excited to the conduction band from the valance band when photons of enough energy falls on it and the number of charge carriers are raised.

2. Extrinsic Photoresistor: ( Types of LDR )

These are semiconductor materials doped with contaminants which are called dopants. These dopants produce new energy bands over the valence band which is filled with electrons. Hence this decreases the band gap. Therefore lesser energy is needed in exciting them. Extrinsic photo resistors are ordinarily utilized for high wavelengths.

Applications of Photoresistor (LDRs)

Photo resistors (LDRs) have low cost and are often used as light sensors. Other applications of photo resistors include:

• Classify availability or unavailability of light like in a camera light meter.
• Used in street lighting design (can be merged with a good Arduino starter kit to act as a street light controller)
• Used in alarm clocks
• Used in housebreaker alarm circuits
• Used in light intensity meters
• Used as part of a SCADA system to implement purposes such as counting the number of packages on a moving conveyor belt etc.

Difference between LED and LDR

An LED (light-emitting diodes) is an electrical element that transforms electrical energy into light energy whereas an LDR uses light to perform the circuit and manage the flow of current .In LEDs the current is permitted to flow in only a single direction whereas an LDR resists the flow of current.