Thanks by the ideas guys, well, let me share some thoughts…
Unless U4 don’t uses HLSL, the light intensity, color and position from all materials are being considered on some stage from pixel shader outputs, so a MAX( , ) or a <= would not be this way heavy to proccess.
I bet these “variables” are protected in some way being either pre-added or post-fixed each time we choose the Material Domains, Blending Modes or Shading Models.
I don’t know if they changed this, but on the old UDK docs Epic explained light environment on pawns with some “planes” floating in the air and Marcus from GoW intersecting with them, and by what I got these “planes” adds or removes light intensity from final results.
I’m just asking to avoid dissecting the entire render code, should be amazing get a simplest “read there!”. LOL