Which component is used to detect light levels, eg in automatic security lights?

Which component is used to detect light levels, eg in automatic security lights?

• A. Thermistor
• B. Capacitor
• C. Light-dependent resistor
• D. Inductor

Answer: (C)

Detecting light levels is done with a component whose resistance changes with illumination: the light-dependent resistor. It acts like a sensor that becomes highly resistive in darkness and much less resistive in bright light. In automatic security lights, this change in resistance is used in a circuit (often a voltage divider feeding a comparator or controller) to decide when to turn the lights on as ambient light drops below a chosen threshold. This is exactly what you need to sense day versus night and trigger the lighting. The other components don’t sense light: a thermistor measures temperature, a capacitor stores electrical energy, and an inductor stores magnetic energy and filters signals.

Detecting light levels is done with a component whose resistance changes with illumination: the light-dependent resistor. It acts like a sensor that becomes highly resistive in darkness and much less resistive in bright light. In automatic security lights, this change in resistance is used in a circuit (often a voltage divider feeding a comparator or controller) to decide when to turn the lights on as ambient light drops below a chosen threshold. This is exactly what you need to sense day versus night and trigger the lighting.

The other components don’t sense light: a thermistor measures temperature, a capacitor stores electrical energy, and an inductor stores magnetic energy and filters signals.