This time it's really worth it to download the latest daily build of Corona Renderer. Recently the gents behind it introduced an awesome feature called LightMixer. Up until now similar stuff was only available in Maxwell and Fryrender (is that still being developed?!), but right now everyone will have access to this incredible thing. Below you'll find a short how-to and you'll also find my notes to that video right underneath.
Ok, based on this video I'm sure you already have a pretty good idea about how this works, but just in case I'll do a small run down.
What is it? Basically Corona LightMixer allows you to control the power of your light sources straight in the frame buffer. It works with both interactive and "regular" rendering so it can be pretty useful.
How it works? Looking at the video above I'm sure you've already noticed that it's basically a render pass, very similar to VrayLightSelect, but one that allows you to control it's multiplier straight in the framebuffer, instead creating a need to comp it in postproduction.
To get LightMixer working you have to create a new CShading_LightSelect pass, scroll down and add all the light sources that you want to control in this particular group, to the Light Select Render Element list by pressing "+" and selecting each light individually.
IMPORTANT! LightSelect pass does not care about instances. If you have 100 lights that are all instanced, you have to select all of them.
The amazing thing is that LightMixer also allows you to change the color of your light sources, but in the end, and this is an important one, you have to remember that this is just a postproduction gimmick, basically combining together different LightSelect passes like you would in photoshop, it won't change anything in your scene, which means that as soon as you'll reset your frame buffer to defaults or merge those lights into a new scene, you'll have to go through that entire process once again.
Still! What an amazingly useful thing! Hope you'll enjoy it.