A fixture with magnetic ballast consumes about 1/3 more input power than
one with an electronic ballast. The extra power translates directly
into heat, so if you're concerned about temperature of the shelf above
or simply want to save energy you should consider an electronic ballast.
An additional benefit of electronic ballasts is higher light output.

A good summary of fluorescent energy use:

http://www.eere.energy.gov/femp/tech...rtube_lamp.cfm

And here's a fluorescent FAQ:

http://members.misty.com/don/f-lamp.html

John