Roberto Casati & Patrick Cavanagh in The MIT Press Reader:
Painters have long struggled with the difficulties of depicting shadows, so much so that shadows — after a brief, spectacular showcase in ancient Roman paintings and mosaics — are almost absent from pictorial art up to the Renaissance and then are hardly present outside traditional Western art.
Here, we embark on a journey that takes us through a number of extraordinary pictorial experiments — some successful, some less so, but all interesting. We have singled out some broad categories of solutions to pictorial problems: depicted shadows having trouble negotiating obstacles in their path; shadow shapes and colors that stretch credibility; inconsistent illumination in the scene; and shadow character getting lost. We also find some taboos, that is, self-inflicted limitations on where or what to depict of a shadow.