Consider Montag's internal conflict about using fire. What two ways of behaving are in conflict?
How does Montag resolve the conflict as he looks at the sun? At the end of the novel, what actions does Montag take that reflect his resolution of the conflict?
At the very beginning of the book we see Montag's obsession and enjoyment of fire and its destruction of books:
It was a pleasure to burn.
It was a special pleasure to see things eaten, to see things blackened and changed. With the brass nozzle in his fists, with this great python spitting its venomous kerosene upon the world, the blood pounded i his head, and his hands were the hands of some amazing conductor playing all the symphonies of blazing and burning to bring down the tatters and charcoal ruins of history.
These first words of the novel express Montag's fascination and attraction to burning, interestingly linking it with power. It is clear that the metaphor used to describe his hands (to a conductor) shows that burning allows Montag to imagine himself transformed into some kind of artist - the power to orchestrate the destruction of "the tatters and charcoal ruins of history" clearly has its attractions to him.
However, the first burning in the novel we are introduced to changes Montag's view and sparks off (no pun intended) the conflict that drives the rest of the novel and his own inner enlightenment. The woman who willingly burns herself, poignantly quoting Latimer, causes Montag to question the destruction of books. This also triggers off the battle for Montag's soul by Beatty and Faber who both attempt to win him over to their point of view.
For me, I would examine a different part of the novel rather than the sun incident. After he has escaped the hound, he undergoes a transformation in his view of fire:
The fire was gone, then back again, like a winking eye. He stopped, afraid he might blow the fire out with a single breath. But the fire was there and he approached warily, from a long way off. It took the better part of fifteen minutes before he drew very close indeed to it, and then he stood looking at it from cover. That small motion, the white and red colour, a strange fire because it meant a different thing to him.
It was not burning. It was warming.
...He hadn't known fire could look this way. He had never thought in his life that it could give as well as take. Even its smell was different.
For me, this passage marks the end of the conflict within Montag, when he realises the other properties of fire - to warm, nurture and protect, rather than simply to destroy. It is this that completes his process of enlightenment and prepares us for his decision to join the group of dissidents at the end of the novel.