Nope, Corona should be quite efficient without them and from my tests, difference is only minor, almost none. Any chance you could post your renders and some description on scene setup?
A few important notes when rendering interior scenes:
1, Always make sure all objects in your scene have enabled shadow casting in objects properties. Disabling shadow casting is a fake, and fakes in Corona affect performance in a negative way. So if you intend to disable shadow casting for example on glass planes in the windows, you can actually make whole situation even worse.
2, if you have any glass in the windows, or any other light entrances to the space you are rendering, make sure geometry of the glass is only one sided (one face, no thickness) and apply glass material with glass mode set to twosided (thin). This mode not only can render objects of very thin glass without need of adding thickness to the geometry (like led lights glass) but also does not affect rendertime at all if you use it in windows.
If you use regular thick glass with refraction in windows, any ray that passes through it is considered a caustics and your scene will take extremely long time to render...
3, For interior scenes, switch secondary GI solver to HD Cache and leave it at defaults, it is going to work well.
Don't use opacity maps for any elements covering windows (like curtains) unless you have really good reason to. For fast rendering, use just translucency and refraction level value with mode set to twosided.
I wrote this because most of the people have problems with slow rendering caused either by having glass in windows, or secondary GI solver set to path tracing on an interior scene. And then they come up with nonsenses like silly portal light, which other renderers implement because their GI solutions suck ;)
Thanks for your very nice suggestions.. I know thread is bit old but the post was quiet useful for me.. So thanks again
I have the same thing to say. And the thing, that I mention it, is because I think somehow we should collect these useful and important guides to the people how are coming here to try out what Corona is capable of (because as I read other forums, I see more and more users checking it out). It can be a Wiki, or something.
For example I have already read some topics here in the forums and I thought I know the basics of this render engine, so I left one of my newly created scenes (created for Corona from the first bit ;) ) to render, but after an all night session (approx. ~7 hours) what I found was a not bad, but definetaly not clean render. And the problems were just some simple things mentioned in the post quoted above.
So I think If we want to persuade the newcomers about the potential that's in this engine we should make some of these simple things (that makes a huge difference in the final render) clear from the first step.
