LDR 5mm

A photoresistor whose resistance drops sharply as light falls on it - typically from megohms in darkness to a few hundred ohms in bright light. Wired with a fixed resistor as a divider it gives an analogue voltage that an Arduino reads directly, making it the simplest light sensor available. This is the 5 mm version, the most commonly used size, and the one most tutorials and kits assume. Note that LDRs vary noticeably between individual parts and respond over hundreds of milliseconds, so they suit ambient light sensing rather than fast or calibrated measurement. Very simple to use with one fixed resistor; Reads directly on an Arduino analogue pin; Wide resistance swing between dark and light; Very low cost for light sensing