This document discusses light dependent resistors (LDRs), also known as photoresistors. It describes LDRs as electronic components that change the operation of a circuit based on light levels. The document explains that LDRs work on the principle of photoconductivity, where light absorption allows electrons to move between bands and increase conductivity. It distinguishes between intrinsic and extrinsic photoresistors, which differ in their semiconductor materials and doping. The construction, advantages, disadvantages and applications of LDRs are also outlined.