What is the main function of a thermostat?

The main function of a thermostat is to regulate the temperature in a system. It acts as a temperature-sensing device that monitors the ambient temperature and activates heating or cooling systems to maintain a desired setpoint. When the temperature deviates from the setpoint, the thermostat signals the heating or cooling system to either turn on or off, ensuring that the environment remains comfortable and energy efficient.

The other options pertain to different components and functions that are not directly related to the primary role of a thermostat. For instance, measuring humidity levels and controlling airflow are tasks typically managed by separate sensors and systems, while providing internal lighting falls outside the scope of a thermostat's function. Thus, the central role of a thermostat is clearly focused on temperature regulation.