I use inexpensive goose-neck lights that you can find at an office
supply store (the kind that have screw-on clamps that can be
modified to be screwed into a block of wood and then held on with an
inexpensive C-clamp). Since a number of shows I do limit the number
of lamps you can have - have to avoid blowing circuits! - I also
help out the display by using white cloth lining in the cases to
help brighten things up.
You might want to stop by your local hardware store and see if they
have a display that shows what different lights look like. The color
of the bulb you use in your lighting can make a big difference in
how your pieces appear to your customers.
The Amethyst Rose