How to create a light wall in after effects? I want to create a wall of lights, that will be animated (on/off) by simple graphics in motion, similar to: 
                
            

So far I created the wall of lights using Optical Flare + AE point lights. I can also "flash" the full wall by animating the brightness of the optical flare FX.

BUT: how can I actually base the brightness of individual lights on eg a graphical arrow or any, as seen in the video linked above?

Can I somehow add a matte/mask to the optical flares FX layer, so that the optical flare FX will only pick the lights that apply to that mask, and change their brightness accordingly?

Or maybe I'd have not to apply as matte animation on the FX, but on the 200 light layers somehow?
Most light walls in AE are made using a matrix of sorts, rather than individually creating many light layers.  Trapcode Form would allow you to create a 2D array of individual glowing particles, which can then be "driven" by another layer, to adjust the brightness of each individual particle.  A lamp image could be used for the particles, and additional glow effects can then be overlaid to make the effect more convincing. 

There's a page here listing lots of different ways of achieving the same effect:

http://provideocoalition.com/ryoung/story/led_and_casino_text_effects_in_after_effects/