A light-dependent resistor is also known as a photoresistor, photoconductor, and photocell. An LDR is one kind of resistor whose resistance differs depending on the amount of light falling on its surface. When the light falls on the resistor, then the resistance modifies. These resistors are often used in many circuits where it is needed to sense the presence of light.
These resistors have different types of functions and resistance. For example, when the LDR is in darkness, then it can be used to turn ON a light and used to turn OFF a light when it is in the light. A common light-dependent resistor has a resistance in the darkness of 1M (Ohm), and in the light, a resistance of a pair of K (Ohm). Pin detail of light-dependent resistor.
Working of LDR
This resistor operates on the principle of photoconductivity. It is nothing, but when the light falls on its surface, then the material conductivity lowers, and also the electrons in the valence band of the tool are excited to the conduction band. These photons in the eventuate light must have more energy than the band space of the semiconductor material. LDR manufactures the electrons to jump through the valence band to conduction.
These tools depend on the light; when light falls on the LDR, then the resistance is low and grows in the dark. When an LDR is staying in a dark place, its resistance is high, and when the LDR is staying in the light, its resistance will be low.
Types of LDR
There are two types of light-dependent resistors, which are as follows:
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Intrinsic Photo Resistors
These resistors are pure semiconductor tools such as silicon or germanium. When the light falls on the LDR, then the electrons obtain excited from the valence band to the conduction band and a number of charge carriers grow.
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Extrinsic Photo Resistors
These tools are doped with pollution, and this pollution makes a new energy band upon the valence band. These bands are filled with electrons. So this decreases the bandgap and a small quantity of energy is needed in moving them. These resistors are fundamentally used for long wavelengths.
Application of Light-Dependent Resistor:
- Used in the security alarm.
- Used in the photosensitive relay.
- It is used in in-camera light meters.
- The LDR is used in optical coding.
- The LDR is used in smoke detectors.
- Used in light-activated control circuits.
- The LDR is used in infrared astronomy.
- The LDR is also used in street light control circuits.
- Used in light failure alarm circuits and used in light meters.
- The Light Dependent Resistor (LDR) is used for automatic contrast and brightness control in television receivers.