During the day, the solar panel converts solar energy into electrical energy and stores the current into the battery through the controller. When it is dark, the battery panel voltage will gradually decrease. When the voltage is less than the voltage specified by the controller, the controller will make the battery supply power to the load gradually brighter that day. The battery board voltage gradually increases. When the voltage is greater than the voltage specified by the controller, the controller will cut off the battery's power supply to the load. This is the light control principle of solar street lights.