Sorry I've been away, but I'm BACK! Here's a look at how to sketch in simple sunlight and artificial light shadows.
Materials used in the demo
Papermate Flair pens http://amzn.to/1BlGxi3
SAX Tracing Paper http://amzn.to/1uv9H7o
Copic Markers http://amzn.to/1ysibmj