''Juliet is the sun'' - Romeo
Metaphor + light imagery - connotes that Juliet lights up his world and brightens his depressed/dark self.
Suggests she makes him happy when he's down
The fact that ''Juliet is the sun'' suggests that like the sun, she will rise and then at some point set (die)
Without light you can't live, suggests Romeos obsession with Juliet is unrealistic/lustful