First of all I'm new here and new to Corona also. It's a very interesting rendering engine and will probably use it in the future for production purposes.
The story of the volumetric lightning, or GI fog, how do you want to call it:
This "little" feature was introduced in a pre-alpha version of Maxwell Render few years ago. Since was demanding large ammount of processing (some little tests with poor quality took even 200h) they took it out and not even today we don't have such a thing.
So it's not about simple fake volumetric light not even close with the fake fog simulated with zdepth channels in PH.
I'm talking about real fog. The one which creates the so called "volumetric light" when the rays spread and illuminate the particles inside the fog and disperse the light in all directions.
So in a real environment a dusty air disperse the light inside the volume. A certain number of rays must be calculated creating particles in the atmosphere.
I'm still waiting, maybe someday, someone, if we are ready, will create a realistic way to simulate this kind of thing. I guess this is the top notch feature and the last one in the whole industry.
PS: if someone tries to convince me it was already made, believe me. It's all fake simulation. NextLimit tried and it was a fail; we dont have computers for such a thing. Not yet, or maybe there could be a different way.
A real VL would expand your rendering time 100x times. Probably. Think about: every soft/reflection will disperse the light in directions which would illuminate particles which disperse the light further and reflect it also back onto surfaces, the fog itself becoming an illuminating source.
In fact the "Volumetric Light" doesn't exist. It's an effect resulted from what I described above. More correct would be GI FOG for example.
