View Full Version : Mr portal light: "FG method" vs black body

07 July 2012, 08:07 PM
How do they compare when simulating light from the outside? Does anyone use black body instead of the standard fg method? Black body method seems to render faster but I'm not sure of this, can anyone clarify? I imagine the fg method uses the sky as the color source and that makes the light a bit varied, but is it that different really?

Sorry for all the random questions, I don't have a fast enough computer to test it out properly. If you have any additional information that would be interesting.


07 July 2012, 05:37 PM
For Portal Lights, there's no reason to use blackbody temperatures really. Portals are FG concentrators and you're going to wants something to concentrate, if you're using blackbody you could just use a regular area light, as this will nullify the purpose and effects of a Portal Light.

07 July 2012, 11:31 PM
Thank you for your reply, but I read here ( and saw in a gnomon tutorial by jeff patton that this method can work nicely since portal lights distribute the light more evenly, like the link shows.

07 July 2012, 12:01 AM
Perhaps you're using Max and not Maya, then?

The mr Sky Portal can be used as a true area light when combined with a Custom color shader and by using the mental ray mib_blackbody shader.

In Maya, which is what I use, we already have "true area lights" for mental ray. So using the Portal Light in conjunction with the blackbody is redundant to begin with, as this just adds an extra node and unnecessary step, as well as superfluous controls which add complexity for no reason, and make it more difficult to diagnose a scene when things "go sour".

The point behind the Portal Light is that it will focus Final Gather (and photon GI if desired) from what's BEHIND the Portal Light. If you're just using it as an area light, there's no reason I can think of to use a Portal Light shader to begin with. That said, the image here: not how mental ray Area Lights behave in Maya, so if that's how they behave in Max, then I say go for it! Use whatever works, of course.

07 July 2012, 08:45 AM
Oh yes, I should have pointed out that I'm a max user. Well that means you are luckier than I am. It doesn't however, help me much, hehe.

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07 July 2012, 08:45 AM
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