There was a stand at Autosport doing an LED illuminated two car pit board affair. You flicked it on and the numbers were say fluorescent orange, then you flicked it into say fluorescent green for another car.
It looked quite effective.
Also see
http://showtrax.net/products/timing-boards with a you tube clip as well
Or
http://www.facebook.com/media/set/?s...1779286&type=3