A light-dependent resistor (LDR), also known as a photoresistor, is a type of sensor that alters its resistance in response to the intensity of light it receives.

LDRs are constructed from semiconductor materials that exhibit photoconductivity. This property means that the electrical conductivity of the material changes when it is exposed to light. Specifically, when light strikes the LDR, the photons impart energy to the electrons in the semiconductor, allowing them to move to higher energy states. This process increases the number of charge carriers within the material, leading to a decrease in the resistance of the LDR. Conversely, when the intensity of light diminishes, the number of charge carriers also decreases, resulting in an increase in the LDR’s resistance.

LDRs find application in a wide variety of fields, such as automatic street lighting, burglar alarms, and camera light meters. In street lighting systems, LDRs are employed to monitor ambient light levels and control the operation of the lights accordingly. In burglar alarms, they detect fluctuations in light intensity, which may indicate the presence of an intruder. Additionally, in camera light meters, LDRs measure the light that falls on the camera sensor, allowing for automatic adjustments to exposure settings.

In summary, LDRs serve as a simple yet effective solution for detecting light levels, making them valuable components in numerous applications.