An LDR works by changing the amount of resistance it produces depending on how much light is hitting it. The more light that hits an LDR, the less resistance it will have. We can use this change in resistance to our advantage by creating a voltage divider.

An LDR has two legs which are connected to separate pieces of metal on its surface.These pieces of metal are separated by a substance called a semiconductor which conducts more electricity when its electrons are excited by the light photons. This substance is usually orange on LDRs, shown in the image below.