how do you light crystal art?

Answer 1

You light it from underneath. Usually there's a glass pane separating the crystal from the light / heat source on which the crystal in placed.

Answer 2

You have two choices. If you can locate a light source under it and mask it so the light only goes through the piece and not generate too much heat, that works well. But it is hard to do with several pieces and non-custom shelves/mounts. So the current method (an improvement on older more expensive choices) is to mount low voltage narrow beam halogen MR16 lights above or above and in front and adjust the beam to the glass, the shelf and back wall being dark grey, blue, or black. There are many, many systems of lighting using these instruments including two bare wires (low voltage), tracks, adjustable arms, etc.
Here is one discussion
http://en.wikipedia.org/wiki/MR16
examples of bulbs
http://images.google.com/images?sourceid=navclient&ie=UTF-8&rls=GWYE,GWYE:2006-47,GWYE:en&q=MR16&um=1&sa=N&tab=wi
and of fixtures
http://images.google.com/images?svnum=10&um=1&hl=en&rls=GWYE%2CGWYE%3A2006-47%2CGWYE%3Aen&q=MR16+fixtures
and a few wire mount
http://images.google.com/images?q=MR16+fixtures+wire+mount&svnum=10&um=1&hl=en&rls=GWYE,GWYE:2006-47,GWYE:en&start=20&sa=N&ndsp=20