mib_portal_light functions as a tool to focus FG rays. At it's most basic level, it can improve performance and quality for the age-old architectural lighting trick of placing area lights in windows. This trick has long been a way to imitate indirect soft lighting from window sources, in an otherwise dark room. Here is an example:
The above image uses 2 area lights scaled to the windows. Each has identical settings, as seen below. I also used a single bounce in my FG options.
So that is pretty traditional. The quality shown is low, so most users would push the FG quality up far beyond default (the above render is defualt FG settings btw). They might also use some FG filtering. Quickly your render tests will become coffee breaks with such wasted rays;)
So now for the portal light. in Maya2008, this is a light shader and should be connected to an area light. Here are the connections.
As shown, connect to both the Light shader and the Photon shader. If you plan to use GI, this is critical. We'll only really need the light shader, but do it anyway, cause it's only right;)
The portal_light now becomes the root of your light control. So I fiddled with the intensity multiplier (set to 5) to imitate the general look of my earlier area lights. The result is below. I've also reposted the original image below the new one, to compare.
You can see the original image has FG issues like discernible ray splotchiness. The new portal image cleans up these issues with roughly the same render time.
Now, what is really going on? The portalLight's greater function is not really being touched on in this tutorial. It is meant to be used in conjunction with an environment input, like physical sky/sun. This will be covered in another post. But here, the portalLight is left without an environment input, so it defaults to a white area light. It acts as a FG focus. normally, FG will send out lots of rays that will only occasionally see the windows. Portal Light can more efficiently focus those rays. In this basic setup, it highly reduces the amount of FG rays you need for a quality architectural render. Thus its value is great, even without going any further. But further we will go...
