An auto light system for automatically controlling driving of a vehicular lamp according to an external light level includes an auto light sensor configured to receive light and detect an irradiance of the light. A controller is configured to compare the irradiance detected by the auto light sensor with a reference value to switch on and off a lamp of a vehicle. An input is provided such that a user performs manipulation for changing the reference value. If the user performs the manipulation input for changing the reference value through the input, the controller receives a signal according to the manipulation input by the user, changes the reference value, and stores the changed reference value.