What is an LDR (Light Dependent Resistor)

The LDR may be a component that features a (variable) resistance that changes with the sunshine intensity that falls upon it. this enables them to be utilized in light sensing circuits.

The most common sort of LDR features a resistance that falls with a rise within the candlepower falling upon the device (as shown within the image above). The resistance of an LDR may typically have the subsequent resistances:

Daylight = 5KΩ

Dark = 20MΩ

You can, therefore, see that there’s an outsized variation between these figures. If you plotted this variation on a graph you’d get something almost like that shown by the graph shown above.

Working Principle of  LDR

This resistor works on the principle of photoconductivity. it’s nothing but, when the sunshine falls on its surface, then the fabric conductivity reduces and also the electrons within the valence band of the device are excited to the conduction band. These photons within the incident light must have energy greater than the bandgap of the semiconductor material. This makes the electrons to leap from the valence band to conduction.

These devices depend upon the sunshine, when light falls on the LDR then the resistance decreases, and increases within the dark. When an LDR is kept within the dark place, its resistance is high and, when the LDR is kept within the light its resistance will decrease.

Applications of LDRs

There are many applications for Light Dependent Resistors. These include:

Lighting switch

The most obvious application for an LDR is to automatically turn on a light at a certain light level. An example of this could be a street light or a garden light.

Camera shutter control

LDRs can be used to control the shutter speed on a camera. The LDR would be used to measure the light intensity which then adjusts the camera shutter speed to the appropriate level.