Because it reflects the radiation back to the lamp. While HPS street lights are working, the electrode materials and electron-emitting materials may cause sputtering. As the amount of spattered deposits on the ceramic tube increases, its absorption of arc and electrode heat gradually increases, and the vapor pressure in the tube increases. The operating voltage of the light source increases. When the operating voltage drops to its normal value after cooling, it can be ignited again. The heat reflected by the reflector will make the voltage increase faster.
Solar street lights will light up at night, but will stop collecting energy, am I right?