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 Light Dependent Resistor (LDR) / Photoresistor

LDR or Light Dependent Resistor (popular as photoresistor) is an electrical device whose resistivity is a dependent on the light falling on it.

In other words they are light-sensitive resistors , Also known as photo-conductive, photo-conductors cells (or photocells), they are made up of semiconductor materials with high resistance values

What does a light dependent resistor do?

LDR (light dependent resistor) are used for detection of light levels, for example, in automatic street and factories lights

They are used in electrical circuit to control lights switching on and off

In the dark hours and low light levels the resistance of an LDR is high and little current can flow through it, while the resistance decreases as the light increases

Value of (LDR) light dependent resistor in dark and light

A photoresistor resistance can vary from about 100Ω in the day light up to 10MΩ in complete darkness

How do you use LDR?

The resistance of photoresistor (LDR) drops in light, which means the current to increase (I=V/R), while in darkness LDR resistance increases.

This variation in value is used in electronic circuits to control a relay which is used to switch on and off the lights

How to test a Photoresistor (LDR)?

by using a digital multimeter a photoresistor can be very easily tested

As mentioned above that the resistance of an photoresistor varies according to the light falling on it, at sun light, the LDR resistance will be around 100 Ohms and at darkness will be around 10M

Does an LDR have polarity?

Resistors have no polarity and the photoresistor (LDR) is just a special resistor type and hence has no polarity that means it can be connected in any direction