Light Dependent Resistor,its types and applications

Light Dependent Resistor,its types and applications

An  light dependent resistor is also known as photo resistor,photo conductor and photocell .LDR is a one kind of resistor whose resistance different depending on the amount of light falling on its surface. When the light falls on the resistor, then the resistance modfies. These resistors are often used in many circuits where it is needed to sense the attendance of light.
These resistors have a different type 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.

Light Dependent Resistor,its types and applications

Working of LDR

This resistor operates on the principle of photo conductivity. 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 energy more 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 well low, and grows in the dark.When a LDR is stay in the dark place, its resistance is high and, when the LDR is stay in the light its resistance will low.

Types of LDR

There are two types of Light Dependent Resistor are as follows:

  • 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 number of charge carriers grows.

  • Extrinsic Photo Resistors

These tools are doped with pollution and these pollution makes a new energy bands upone the valence band.These bands are filled with electrons. So this decrease the band gap and 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 photosensitive relay.
  • It is used in camera light meters.
  • The LDR is used in optical coding.
  • The LDR used in smoke detectors.
  • Used in light activated control circuits.
  • The LDR is used in the infrared astronomy.
  • The LDR also used in street light control circuits.
  • Used in light failure alarm circuits and used in light meter.
  • The Light Dependent Resistor (LDR) used for automatic contrast and brightness control in television receivers.

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