How do I explain the motif of light verses darkness from act 1 scene 5 in Romeo and Juliet?

In act I, scene 5, Romeo first lays eyes on Juliet at the Capulet ball. He sees her as a stunning light, and in contrast, everything else becomes darkness. As he says:

Oh, she doth teach the torches to burn bright!
It seems she hangs upon the cheek of night
Like a rich jewel in an Ethiope’s ear ...

In other words, she is brighter than torches: she teaches them from her example how to burn more brightly. She also sparkles like a jewel against the night. Romeo expresses her beauty as a form of brilliant light.

For Capulet, it is physical light which bring joy to his party. He asks more than once for

More light, more light!

And later, Lord Capulet asks for more torches.

As can be seen, this is a light filled scene, and the light reflects a time of exuberance and happiness. Capulet does all he can to quell unhappiness and anger, for instance by forbidding Tybalt to cause trouble over Romeo, a hated Montague, having crashed the party. Meanwhile, Romeo, newly lovestruck, describes his beloved as as brilliant light.