The ultraviolet energy shield is Goa'uld technology left behind on P3X-513. A pair of devices creates an energy shield which turns the sky orange and protects the inhabitants from dangerously high levels of solar radiation, allowing them to leave their caves during the day. The device had long been buried and forgotten, and the inhabitants had become nocturnal cave dwellers, however, when SG-1 located and restored the pair of devices, the natives were able to live outside the caves once again.
Cross Reference: Captain Conner, Jonas Hanson, Jamala, P3X-513
Episode Reference: The First Commandment