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My emitters just stopped working for some reason. They were working fine earlier today. I tried restarting SU, rebooting my workstation, re-installing the plug-in with no avail. Emmitter materials just render with a weird diffuse color on them or black and do not create any light. Its very strange and has me stumped.

Craziest thing is that if I open my file that was working earlier today, the emitters work. If I copy and paste the emitter into a new file, nothing!

As I wrote in the other post, I don't know of any reason for that to happen, but I can't say much without seeing a file that reproduces the issue. You have checked the standard things, I assume -- disabling the environment and adjusting your exposure, in order to see if your emitters are actually not emitting, or if it is more the case that they are, but are doing so with unexpectedly low power. Also, when you write above about copying/pasting the emitter, are you referring to the emitter material, or some geometry that has such a material assigned to it? Either way, what is the overall scale of the model you are copying from, vs the one you are pasting into? Is it reasonable to believe that the pasted emitter/geometry would be detectable to the camera at the scale of the new document?

As I say, the quickest thing would probably be to upload a file, so I can tell you what you're looking at, and/or if there is some bug in play.

Turns out that is was a backface material issue. I did not realize that your backface needed to be set to the SU default material in order for an emitter to work.

I still don't understand, because there is no rule like that. There are two factors in play, which apply to materials in general, and not emitters specifically:

1. Output > Face Materials; the options are: Use front or back, or Use front only.
2. When no material is found, one may be inherited from a containing group or component.

As such, here is a case in which removing the material from the back of a face would cause it to emit light:

1. Output > Face Materials is set to Use front or back.
2. The face has no material on its front, and a non-emitter material on its back.
3. The face is contained in a group/component that has an emitter material applied.

Removing the face's back material causes it to inherit the material of its parent entity. Is this what happened?

That scenario happens quite alot in Sketchup, I've run afoul of it myself (which is why I adopted/advocate the standard of using front face only for materials/textures).

I would assume the only easy fix would be for Maxwell to support materials on both sides like SketchUp does... which I think would open other interesting possibilities as well.

Best,
Jason.

Any chance they are IES or referencing IES files (MXM's with linked IES)?

Because IES are directional, I've noticed some quirks when I use those and the "flip along...axis" commands. Of course, I also have to be careful of my face orientation.

I've also had issues in previous versions (haven't checked with the most recent update), with components and emitters, though I think that was fixed.

Support for mirrored emitter geometry was added in 2.6.10. I would have to check -- I'm not immediately sure how IES would be affected, if at all.