Try CC Ball Action, play around with ball size and grid spacing.
Johnny Cuevas, Editor
"I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work."
---THOMAS EDISON on inventing the light bulb.
Depending on how realistic you need this to look, there are a couple of methods I can think of.
I did something similar recently using Trapcode Form, with a grid of sphere particles and a precomp driving the opacity and colour values for the particles. As this was part of the background of a fast-moving animation, I didn't worry to much about making it very realistic, but it looked pretty good.
An other method I've seen is to use a grid of lights, and then use expressions to sample the precomp with the content for the light wall to drive the colour and luminosity of the lights. It looks great, but the number of lights can slow even powerful machines to a crawl! There's a really detailed tutorial here: http://qubahq.com/2010/08/tutorialpreset-light-wall/