The basic function of PDRCs is to be high in both solar reflectivity (in 0.4–2.5 μm) and in heat emissivity (in 8–13 μm), to maximize "net emission of longwave thermal radiation " and minimize "absorption of downward shortwave radiation." PDRCs use the infrared window (8–13 μm) for heat transfer with the coldness of outer space (~2.7 K) to radiate heat and subsequently lower ambient temperatures with zero energy input.