Brightness auto control system

PURPOSE: An automatic luminance control system is provided to prevent an accident, by enabling a control part to control the luminance of a tail lamp according to a visual range. CONSTITUTION: A light emitting part(110) emits light. A light detection part(120) senses the light emitted from the light emitting part. A computation part computes the visual range through the light. A transmission part transmits the computation result of the computation part. A wireless terminal device is installed in a vehicle.