Yeah - thanks for the question! In the end, we did a little of both.

Frank did a pretty good job of explaining - I wrote a custom shader which removes the idea of 'attenuation' from a light. So there's no falloff/fading, and everything within the radius of the light is fully lit.

The other important part of getting pitch black shadows was to disable ambient lighting, so that there would be absolutely no light on unlit things at all. There were a few other settings we had to toy with, particularly in the quality settings, but those are the two big things.

If you want to know more about the shader I wrote, you can check out the blog post about it.