4.4 Introduction to LDR sensor

What is a LDR?

A  light dependent resistor (LDR) also called as photoresistor or photoconductor is basically a photo cell which works on the principle of ph0toconductivity.

It is used to detect the levels of lights.For example automatic street light, when the light intensity increases ,the resistance decreases and when their is low light level at that moment the Resistance of a LDR increases and small amount of current flow through it.

In LDR, resistor is the passive component whose resistance decreases when the intensity of light is decreases and this optoelectronic device is used in the light varying circuit & light and dark switching circuits.

Pin Configuration:

LDR sensor module have 4 pins:

  1. VCC
  2. GND
  3. Digital Output(D0)
  4. Analog Output(A0)

Working of LDR sensor:

When light intensity increase on the surface of the LDR then the resistance of the LDR decreases and at this time the threshold voltage(which is the minimum voltage) is greater than the input voltage,So, the sensor output goes LOW.

When light intensity decrease (low/dark) on the surface of the LDR then the resistance of the LDR increases and at this time the input voltage(which is the minimum voltage) is greater than the threshold voltage,So, the sensor output goes HIGH.