How Does an LDR Work?

Light dependent resistors, or LDRs, work by adjusting the amount of current flowing through a circuit in response to the relative abundance of light present in or near a circuit. As the amount of light falling on a light dependent resistor changes, it alters how much it resists the flow of electricity.

Light dependent resistors are frequently used in light detecting devices or those that measure the amount of light present. They are used by a number of different types of professionals, including those involved in security, photography and science.

In some ways, light dependent resistors are similar to other forms of resistors. They change the amount of electricity flowing through a circuit in response to some stimulus. In a potentiometer, such as a volume dial, the stimulus is the dial that the operator turns. For a light dependent resistor, the stimulus is the light level. Light dependent resistors may be designed to stop all electric flow when light is not striking them, or they can be used to gradually reduce the amount of current proportionally to the amount of light striking them.

Also called "photo resistors," LDRs often exhibit a delayed or latent response to light sources. Different photo resistors are designed for different wavelengths and intensities of light. Plated electrodes are the structures inside the resistors that are sensitive to the light energy.