Abstract: The invention is directed to a sensor for measuring light intensity. In one embodiment, the sensor includes a light sensor and an assembling device for attaching and allowing the dismantling of the sensor to a monitor wherein the sensor measures the light intensity generated by the monitor's screen. In another embodiment, the sensor may include an assembling device that connects to a monitor through mould-based connection or magnetic connection. In various embodiments the sensor may also include a linking device and an electronic control device wherein the linking device transmits the measurement data of light intensity to the electronic control device and has an operating radius that is large enough as to allow the positioning of the sensor on any part of the monitor's screen.