Working principle of an LDR:

Semiconductor Material: LDRs are typically made of semiconductor materials, such as cadmium sulfide (CdS) or cadmium selenide (CdSe). These materials exhibit a property called photoconductivity, which means their electrical conductivity changes when exposed to light.

Resistance Variation: When there is little to no light shining on the LDR, its resistance is high. In other words, it does not conduct much current. This state is often referred to as the “dark resistance” or “high-resistance state.”

Light Exposure: When light falls on the surface of the LDR, photons from the light excite electrons within the semiconductor material. This extra energy allows more electrons to move freely, reducing the resistance of the LDR. Consequently, it becomes more conductive and allows more current to flow.

Inverse Relationship: The relationship between the resistance of an LDR and the intensity of light is typically inverse. That is, as the light intensity increases, the resistance decreases, and vice versa. This property allows LDRs to be used as light sensors.