In Chapter 8 of Lord of the Flies Piggy is the one that lights the fire. Why is this significant?

This event is significant because it signifies a growing
acceptance of Piggy amongst the boys and a recognition of how his skills, in particular
his intelligence, is useful and a valued contribution to them all. In this chapter,
after Jack has left the boys in a fit of rage at not being selected to be the leader,
Ralph appears to be rather shocked and needs the support and intelligence of Piggy to
keep focussed. Piggy reminds him of the priority of starting a new fire, and voices the
idea of moving it to the beach. The text tells us that "Only Piggy would have the
intellectual daring to suggest moving the fire from the mountain." Once the fire is
built, note what the text tells us about Piggy lighting
it:

For the
first time on the island, Piggy himself removed his one glass, knelt down and focused
the sun on tinder. Soon there was a ceiling of smoke and a bush of yellow
flame.

Now that Jack has
chosen to remove himself from the group of boys, Piggy seems to have risen in
importance, and this action of his in lighting the fire for the first time signifies
this.