RTX cards might maybe be able one day to preview lightmaps in real-time, possibly, if Epic makes it a real feature in the release editor. It’s not official and I don’t think we know exactly how it will work if it’s made official. GPU Lightmass is an alternative tool for offline baking on the GPU, it doesn’t render the same as regular Lightmass, and is also not official.
Right now, for production on a game that you’re doing today, regular Lightmass is the only thing you can count on, so CPU.
There’s known limitation with GPULightmass’s ray tracer about translucent (GI) shadows. If this becomes popular I may consider adding an alternative path for it, but definitely comes at a not-so-small perf impact.
Thanks for the quick answer.
Maybe i got it wrong, but at the moment im trying to get a baked shadow from a static (!) skylight (hdri) out of a translucent mesh with a translucent material set up (like explained in the unreal docs). only with direct lights i can generate shadowing. with image based skylight rendering there is none.
Think about a hall with a glas with 50% opacity roof with metal strives, which should have a baked lighting by a static skylight hdri. at the moment the scene is lit, like there is no shaded roof top.
another question is the apperiances of these black splotches. although the uv maps for lightmaps are correct, after “merging” meshes, every identical mesh although on a individual position, has the the same form of a splotch. are there informations, how to avoid these?
thank you so much and greetings from europe
4.21 for Christmas
Would be nice to get it almost right after 4.21.1 hotfix (release of which might happen next week) 
Based on popular demands I’ve uploaded a 4.21.0 compatible version. It also supports new Turing cards, but not using hardware ray tracing.
EDIT: There was a quality bug in the first version, if you downloaded it before seeing this edit please update.
EDIT2: I forgot to disable debugging mode and it was slower, now this is fixed and you may want to update.
Yes !
thanks for that 
Amazing news, thanks for the update!
Many thanks your truly a big help to the community,…
Thanks a lot for the 2.21 version ! Would be interesting to see a direct comparison between 1080ti and 2080ti. Although without specific optimization for the Turing architecture, I doubt there will be a huge gap.
Thank you for 4.21, now I can move my projects to it. Hopefully this forum isn’t driving you insane with demands on this spare-time project
Just noticed I was pasting GPU lightmass files in the wrong directory all along. Now I’m experiencing the power of GPU lightmass and it’s amazing. Can’t wait for the new version you’re working on!
Trying for the first time GPU lightmass, ouh boy is this a awesome tool…
I have two questions about GPU lightmass… two problems or issues not sure how to call them.
The first two or three times i have used GPU lightmass it took me like 5 to 6 mins for a whole scene to bake, than out of the blue without changing anything it takes now 11 to 15 mins. Not sure what has actually more than doubled my baking time.
Pointlights, Spotlights and directional lights are way more strong with GPU lightmass, is that right ? I used a view 300 lumen lights in my scene “CPU lightmass” since GPU lightmass i need to put them on 25 to 30 and even than the scene is much brighter than before. Has something changed in the light intensity or light bounce with GPU lightmass ?
And again, amazing tool, many thanks for that!
I have a simple question.
I’d like to know what settings are available from the lightmass rollout in the world settings while using the gpuLightmass. And if nothing from there is actually used in the gpuLightmass, I’d like to know what other settings do I need to tweak to get better quality.
Thanks
I’m having an issue here. After I bake the lighting I’m getting followed by litteral darkness, as you can see on the bottom of the screen. However, I can still see the floor.
And when I launch the game, the floor is pitch black (different from viewport).
Holy c r a p , what a great news today 
Thanks , was unexpected
Fixed my issue, it wasn’t related to GPU lightmass. My floor was a single big chunk, so the UVs were all over the place.
question i have not kept up to date with this for a while. Does this support LODS and espeacially HLODs?
It appears not to support HLODs - correct me if I’m wrong . Since switching to GPULightmass my HLODs are showing up black.
Hi Its notworking on my rtx video card,…?