We've done a lot of racing under the lights at my club actually. At Sammy's track now we have a lot of light cast by his little model train lights around the track. On the track we used to race on we only had 1 very dim light and nearly all of the light for driving was cast by the headlights on the cars themselves. We found that times got a lot slower but... oddly... my times didn't drop quite as much and I was able to win a few races under the lights there.
Sam's track:
http://snsspeedway.blogspot.com/I'm sorry but i'm not able to find any photos i've done of night racing there...