What is the explanation of the metaphor "bloomed with light" in this excerpt from The Great Gatsby?
The Buchanans’ house floated suddenly toward us through the dark, rustling trees. Tom stopped beside the porch and looked up at the second floor where two windows bloomed with light among the vines.
In Chapter Seven, after Tom and Jordan and Nick stop at Wilson's Garage and discover that Mrytle has been run over by Gatsby's yellow car, Tom talks with the police, establishing his innocence by stating that he has driven a blue coupe from New York. But, the "tears were overflowing down his face" over the death of his mistress.
After reaching East Egg, the Buchanans' house "floated suddenly" toward Nick and the others in the coupe. Once out of the car, Tom searches the upper level of the house and finds that "two windows bloomed with light among the vines." Thus, Tom realizes with relief that, although his lover has died, his wife is not harmed. Much like the green light that Gatsby watches in hopes of rediscovering Daisy for his own, Tom Buchanan seeks the light of Daisy's bedroom, with Mrytle now all but forgotten in his fear of his or Daisy's involvement with her murder. Interestingly, Nick notes, "A change had come over him and he spoke gravely...."
Later in the chapter Nick finds Gatsby outside the Buchanans' kitchen window, and he observes,
They weren't happy, and neither of them had touched the cicken or the ale--and yet they weren't unhappy either. There was an unmistakable air of natural intimacy about the picture and anybody would have said that they were conspiring together.
Among the "vines" of his philandering, Tom Buchanan comes home to the "light" of Daisy, his wife. The change that comes over him is his return to his marriage and the commonality he and Daisy share as superficial upper class socialites, who must, above all, protect their reputations and property. "Careless people" that they are, they conspire to protect themselves and sacrifice Gatsby in their place as he unknowingly stands in their yard "watching over nothing."