Is this a prototype for an eventual game? Or is it for a pre-created non-interactive animation? If it's not ever meant to be interactive, then I'd suggest getting into After Effects. For example, searching for "after effects cross hatch": https://www.youtube.com/watch?v=gsCuC6Qytm8
I was expecting an answer like that. Group masks are out because the light has to effect a deep shadow layer more than the faint shadow layer ironically. Here's an example from the tutorial site. Imagine the light pulsing and pushing the linework around like shadows. That's the effect I'm after.
That's very cool. If you plan on doing it in real-time (with Unity, for example), you'll need to use a post-processing shader. You can pack 4 different patterns on a single RGBA image, since the only thing you care about is their transparency (the alpha channel). So with just two small seamless textures (32x32 or something…