This invention is a creative device for reducing the electric power consumption of vehicles?? headlamps. The device can detect the brightness around a vehicle actively while the vehicle stopped at the (red) traffic light in the evening. Once the environment around the vehicle is bright, the device reduces the brightness of vehicle headlamps moderately to save energy. If the vehicle is restarted, the brightness of headlamps will be restored to normal conditions immediately to ensure safe driving. The invention can be applied in vehicles commonly to reduce the electric power and gasoline consumption.