In Chapter 6, SamnEric report a sighting of The Beast for the first time. The Beast, which is really the dead pilot, is first seen by the light of the fire in the middle of the night. SamnEric bring this news to Ralph's tent, and as dawn breaks, he calls the assembly. The description of the sunrise is quite beautiful: "Ralph looked for a moment at the glowing slice of gold that lit them from the right hand and seemed to make speech possible" (Golding 76). There are two ways to interpret this symbolism: the obvious and then the subtle.
The Obvious: Traditionally, light has been associated with goodness, purity, and knowledge. In this case, the meeting begins at dawn, meaning that the knowledge of The Beast is spread to the boys with the light. In the day, the island seems safer and less threatening than at night in the dark, and this safety and knowledge is associated with light (and therefore goodness).
The Subtle: Now here is the tricky thing - the knowledge that Ralph is spreading is actually not true. It is based on the ignorance and fear developed in the dark. However, since the knowledge is being spread with the light, it seems legitimate.
TL;DR The obvious answer is that light means goodness and knowledge, but there is a much more insidious reading of the passage.