How do I make mesh lights (emission shader) work in EEVEE?

This topic has 17 replies, 4 voices, and was last updated 6 years, 2 months ago by Jonathan Lampel.

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June 12, 2020 at 1:25 am #12201
Ingmar Franz
Participant
@jlampel Maybe I’ve just missed in this chapter, but could you please explain how I can make mesh lights (emission shader) work in EEVEE?
June 12, 2020 at 3:52 am #58261
spikeyxxx
Participant
I think you need an Irradiance Volume:
June 12, 2020 at 4:09 am #58262
Ingmar Franz
Participant
Thanks, @spikeyxxx, once again 😀.
June 12, 2020 at 4:25 am #58263
Ingmar Franz
Participant
It works:

But when I tilt the plan, I get some wired shading errors:

I probably have to tweak the settings for the irradiance volumes or change the dimensions and the position of the light probe cuboid. File is here.
June 12, 2020 at 4:30 am #58264
spikeyxxx
Participant
I’m not very good with Eevee, but it looks to me, that you might need a higher resolution of the volume…
June 12, 2020 at 4:59 am #58265
spikeyxxx
Participant
If I remember correctly, you shouldn’t have light probes outside the room/below the plane. The ones below the plane wouldn’t get any light any way..

Maybe the Irradiance Smoothing could help as well?

Jonathan Lampel will surely know more!
June 12, 2020 at 7:46 am #58266
Ingmar Franz
Participant
I’ve reduced the grid in Z-direction to 1 and set “Irradiance Smoothing” on the “Render Properties” tab to “1”:

With a tilted plan, I still get white spots allthough there is not other light than the mesh light:

The ground plane only has the default material.
June 12, 2020 at 8:05 am #58267
spikeyxxx
Participant
I do not understand this!

I’d at least expect the right and left side of the rotated plane to be lit the same…

…but the left side is more greenish and the bottom left appears to be see through…

I think I’m spoiled by Cycles…
June 12, 2020 at 8:17 am #58268
Ingmar Franz
Participant
Hm, I think I have the solution: The white we’re seeing is from the ground plane itself in its original orientation. The light probes took each a 360 degrees image around them during the baking process. Now, these probes are acting as projectors of the situation before the rotation of the ground plane. We’are simply to much used to thinking the way Cycles works.
June 12, 2020 at 8:38 am #58269
Ingmar Franz
Participant
Commands back! There was a white point light hidden from preview but not from rendering. Due to the fact that the camera icon for enabling/disabling the rendering of an object isn’t visible in the “Outliner” per default, I forgot to disable the point light. Now it works as expected:

But parts of the white light before nevertheless originated from the light that the (default material) grey plane reflected in its original orientation.
June 12, 2020 at 8:47 am #58270
spikeyxxx
Participant
Oops. I must be loosing it; I thought I checked that Point Light, but that was indeed only the Viewport visibility, not the rendering (both are sort of square-ish icons…I always have that render icon visible in my files, but loading someone else’s file per default loads their UI and that messes me up sometimes, when I don’t realize that;)
June 12, 2020 at 9:03 am #58271
Ingmar Franz
Participant
Another point with Eevee is that the light baking isn’t yet for animated mesh lights:
June 12, 2020 at 10:45 am #58272
Jonathan Lampel
Participant
Nice, thanks @spikeyxxx ! You’re spot on. I generally don’t use mesh lights at all when rendering with Eevee since the result will always look a bit grid-like, but I’m sure it’s helpful in some situations.
June 12, 2020 at 11:05 am #58273
spikeyxxx
Participant
You’d need to bake the indirect light per frame and that is not (yet?) possible.
June 12, 2020 at 2:19 pm #58274
Ingmar Franz
Participant
Interesting facts the Blender 2.83 manual:

As of now the light cache is static and needs to be computed before rendering. It cannot be updated per frame (unless via scripting). This limitation is being worked on and will be removed in future versions.
l

Hm, I’m wondering how this scripting stuff works 😉. Allthough I have some Python knowledge, I haven’t dived in very much.
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