Light Detection Sensor is Light Dependent Resistor or Photoresistor, which is a passive electronic component, basically, a resistor which has a resistance that varies depending on the light intensity. A photoresistor ( Light Detection Sensor ) is made of a high resistance semiconductor that absorbs photons and based on the quantity and frequency of the absorbed photons the semiconductor material give bound electrons enough energy to jump into the conduction band.

Working principal of Light Detection Sensor:

A light dependent resistor works on the principle of photoconductivity. Photoconductivity is an optical phenomenon in which the conductivity of the material is increased when the light is absorbed by the material.

When light falls i.e. when the photons fall on the device, the electrons in the valence band of the semiconductor material are excited to the conduction band. These photons in the incident light should have energy greater than the band gap of the semiconductor material to make the electrons jump from the valence band to the conduction band.




  • LDR’s have low cost and simple structure.
  • Used in street lamps, alarm clock, burglar alarm circuits, light intensity meters, for counting the packages moving on a conveyor belt, etc.


  • Resistance: 400ohm to 400K ohm.
  • Normal resistance variation: 1K ohm to 10K ohm
  • Sensitivity: about 3 m.sec
  • Voltage ratings: I used it on 3V,5V, and 12V.


LDR Pin Description

The Light Dependent Resistor (LDR) is just another special type of Resistor and hence has no polarity. Meaning they can be connected in any direction. They are breadboard friendly and can be easily used on a perf board also. The symbol for LDR is just as similar to Resistor but adds to inward arrows as shown above. The arrows indicate the light signals.

Materials required:

  • Arduino
  • LED
  • LDR (photoresistor)
  • 220 and 10k ohm resistors
  • Wires
  • Breadboard

Connection with Arduino: