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View Full Version : Broken Area Light behavior in Maya Mental Ray.

Kel Solaar
03-03-2011, 01:06 PM
Hi guys,

I'm encountering some weirdness with Mental Ray Area Lights at the moment, maybe some will be able to shed some light on that !

I did a scene with the following stuff :


Area Light
Area Portal Light
Emissive Plane
Ground


The different emitting objects (Area * Lights and Emissive Plane) have the same size and placed above the ground. The reference for me is the the Emissive Plane. Here are some renders now :

Scale 1.0 on emitting objects :

Emissive Plane
http://kelsolaar.hdrlabs.com/sIBL_GUI/Support/Softwares/Maya/Support/Pictures/Plane_Light_1.0.jpg

Area Portal Light
http://kelsolaar.hdrlabs.com/sIBL_GUI/Support/Softwares/Maya/Support/Pictures/Area_Portal_Light_1.0.jpg

Area Light
http://kelsolaar.hdrlabs.com/sIBL_GUI/Support/Softwares/Maya/Support/Pictures/Area_Light_1.0.jpg

Pretty much the same results, lets move on.

Scale 10 on emitting objects :

Emissive Plane
http://kelsolaar.hdrlabs.com/sIBL_GUI/Support/Softwares/Maya/Support/Pictures/Plane_Light_10.jpg

Area Portal Light
http://kelsolaar.hdrlabs.com/sIBL_GUI/Support/Softwares/Maya/Support/Pictures/Area_Portal_Light_10.jpg

Area Light
http://kelsolaar.hdrlabs.com/sIBL_GUI/Support/Softwares/Maya/Support/Pictures/Area_Light_10.jpg

Mmmhh Area Light doesn't react as I would expect, I do a quick brainstorming and decide to multiply the intensity by the square of scale (100) in this particular case and here is the picture :

Area Light Tweaked Intensity
http://kelsolaar.hdrlabs.com/sIBL_GUI/Support/Softwares/Maya/Support/Pictures/Area_Light_10_IntensityTweak.jpg

Ok we are back in business :) Now I decide to try scaling down, See next post :)

KS
Kel Solaar
03-03-2011, 01:09 PM
Continuing the previous post :

Scale 0.1 on emitting objects :

Emissive Plane
http://kelsolaar.hdrlabs.com/sIBL_GUI/Support/Softwares/Maya/Support/Pictures/Plane_Light_0.1.jpg

Area Portal Light
http://kelsolaar.hdrlabs.com/sIBL_GUI/Support/Softwares/Maya/Support/Pictures/Area_Portal_Light_0.1.jpg

Area Light
http://kelsolaar.hdrlabs.com/sIBL_GUI/Support/Softwares/Maya/Support/Pictures/Area_Light_0.1.jpg

Area Light seems to do funky stuff again ... I divided my scale by 10 so I'm assuming it will follow the same behavior than when I scaled up, so I multiply my intensity by square of 0.1 (0.01) And here we go :

Area Light Intensity Tweak
http://kelsolaar.hdrlabs.com/sIBL_GUI/Support/Softwares/Maya/Support/Pictures/Area_Light_0.1_IntensityTweak.jpg

Cool I don't see anything now ... Wtf? :) I decide to crank up the intensity a bit to see what's going on inputing 0.1:

Area Light Intensity Tweak Alternate
http://kelsolaar.hdrlabs.com/sIBL_GUI/Support/Softwares/Maya/Support/Pictures/Area_Light_0.1_IntensityTweakAlternate.jpg

??? What's happening with the decay ? It seems to cover a larger area than expected.

So basically, has somebody a solution for this ? The problem I have with the portal light, is that it reacts to FG, and can't use a disc shape if I'm right. The scene is attached to the first post.

KS
InfernalDarkness
03-04-2011, 03:43 AM
Simply turn off the FG interaction in your Portal Light. If that's not good enough, use the miFinalGatherHide attribute on your Portal Light.
Kel Solaar
03-05-2011, 02:26 PM
Thank you Sho,

I'll give a try at this, though my main concern is more about the Area Light itself :)

KS
CGTalk Moderation
03-05-2011, 02:27 PM
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