By light he means Deadlights, Pennywise's true form. The spider is his avatar in the physical world. But I can't prove it to you directly because chapter 22 is quite long. However, in the mentioned place, Pennywise is destroyed and they do this thanks to the power of ChĂĽd (a power ritual equivalent to High 1-A) However, in the novel The Insomnia, which tells the chronological story of what happened after this event, it is revealed that the Deadlights were not destroyed. This does not directly indicate that he was regenerated, but he did survive the first ChĂĽd ritual. Therefore, logically, it must have returned in the second ritual, renewed like the first ritual.