Just keep the lighting over the tournament machines up high enough so that people don't need to use headlamps. Dim is bad there, you're playing for keeps, not for the mood. Ideally, the free play area should be a mix of dim and not-dim, since people have different opinions on how bright they like it when they play. That's harder to manage, though; it works better to have "dimmer hours", e.g. have the lights brighter during the day and then lower after some time in the evening like 8 p.m. I've been to shows that have done that in the past, it works well.