Candles and Light in the Merchant of Venice

In a few weeks I am giving a talk to a small group of women. We meet regularly and take turns hosting and talking to the group. This year's theme is light. I chose to give the November talk because it is near my son's birthday and Hannukah. I am planning on talking about the use of candles to celebrate occasions and the symbology of lighting candles to repel darkness and the idea of smoke carrying wishes and prayers to gods.

As a title to my talk I chose Portia's quote in Act 5, Scene 1: "How far that little candle throws his beams!/ So shines a good deed in a naughty world." I wanted to give a little context to this quote as part of my talk, but it has been several years since I read Merchant of Venice. I was wondering if anyone on this list has thoughts about Shakespeare's use of light and dark and/or daylight and nighttime in this play. I am planning on rereading the play, but if anyone out there has links to other articles on this topic or ideas about where to find them I would greatly appreciate it.

This is a fairly casual gathering, so I don't need long treatises, but some context would be wonderful.

Thanks for your help.