A light sensor is an electronic device designed to detect and measure the intensity of light in an environment. It can sense visible light, and in some cases infrared or ultraviolet radiation, converting the light level into an electrical or digital signal that can be used for monitoring, control, or automation purposes.

Light sensors operate based on changes in electrical properties when exposed to light, utilizing technologies such as photoresistors (LDRs), photodiodes, phototransistors, and ambient light sensor (ALS) ICs. Depending on the sensor type, they can perform basic light/dark detection or provide precise measurements of illumination, typically expressed in lux.

Modern light sensors are compact, highly sensitive, energy-efficient, and capable of real-time data output, making them suitable for integration with IoT platforms, automated systems, and smart devices.

Light sensors are widely used in smart lighting, mobile devices, display brightness control, security systems, environmental monitoring, and energy-efficient building automation, where accurate light detection enhances safety, comfort, and operational efficiency.