We tried to play glow-in-the-dark volleyball a couple of months ago.  Here's what we learned. Black lights are hard to find (at least in the Washington Area) and pretty pricey. Our initial plan was just to have some lamps with black light bulbs but you can't have exposed bulbs in the church. They have to be protected by a cage. So the Young Women's president just ended up getting glow-in-the-dark necklaces and bracelets for everyone and we left the doors open a crack. The ball was painted with glow-in-the-dark paint, but it didn't last long and we kept having to stop to "charge" the ball with a big flashlight. I wasn't our most technically successful activity ever but the youth still had a blast and want to do it again. Next time we are going to try to get a hold of some of those garage lights that you can hang from the hood of a car, they have a cage and you could hang them up high. We figured you'd probably need 3-4 lights.

Another idea:  Make sure you wrap the balls with reflective tape that will glow in the dark, and have the youth wear white shirts and socks.