Here are some tests, settings are from message but:
Added a sunlight ( intensity 6, indirect lighting 3 )
Skylight ( intensity 0.5, indirect lighting 3 )
Post process tweaks: enable GI with a value of 3
Render time: 2:03 hours on Production
Awesome thread, lots of interesting stuff! I would also love to see those .ini settings exposed to the editor- perhaps under “advanced lighting” options to not confuse those who are just looking for the basic parameters! It’s fine tweaking the .ini file manually, but it does get quite tedious and it would make the in editor settings feel much more complete if they were added!
Oh nice! Portal Lights- sweet, can’t wait for the public implementation. great work -
I’ve just built my whole 2000+ meshes scene in 59 mins by reducing the scale to .4 (lightmaps res 1024) and leave indirect lighting quality to 1. Previous attempt with quality 6 and scale .15 took 16 hours. (with lightmaps of 256). Stunning. It looks way better now and took 1/16th of the time!
@Nicolas3D : What I have observed is, if we are using other lights along with Skylight we don’t need the high Photon Density(Direct as well as Indirect). Increasing the Photon Density, increases the build time by the factor of amount of increase from default value(400).
@ : Please correct me if I am wrong.
In your scene, you can get the same quality with the following settings with reduction of build time by around 60%:
Use default BaseLightMass.ini with only NumHemisphereSamplesScale > 64
Static Lighting Level Scale: 1
Num Indirect Lighting Bounces: 100
Indirect Lighting Quality: 10
Indirect Lighting Smoothness: 1
You can play with Indirect Light Intensity of SkyLight and Directional Light to get this quality with much faster Build time.
@: It took around 40 mins for light build. Also I have observed that these values differ substantially depending on scene. If scene has lot of closed space, as in case of Interiors, it is very difficult to get good lighting with only Skylight even with lot of changes in BaseLightMass.ini.
Thanks for the tips 
I was about to build the scene with NumHemisphereSamplesScale > 400 at Medium quality, but I notice that the build time was incredibly slow, so I guess I’ll try a lower value for that.
@: based on Rafareis reply and by some tests the scale is what gives you the soft shadow details from large/small objects and it makes quite the difference, and of course it increase the build time, not entirely sure how much since I mixed the values between tests.
With 0.15/0.25 the shadows quality is really good, but the value also depends on the scene itself and the degree of detail you want.
@: Are portals going to be included in a release soon? 
great test !!
thanks all
Just a quick question: Where can I see how long my build time is? Are you guys sitting next to your computer for 4 hours or is there a timestamp somewhere? Thank you!
In the Output Log. (window->dev tools->output log)
Open up Swarm Agent. Go to “Log” tab. You will get all details.
Just weighing in on this badboy (awesome thread, gutted I didn’t find it sooner).
One major improvement I’d like to see to lightmass is an improvement to the map processing. Currently it’s not possible to divide a single texture up across multiple threads, so build times are always capped at the largest lightmap resolution you have in the scene (usually anyway), and only one thread can do that work while the rest are doing nothing. Something similar to xNormals method where lightmaps are processed one-by-one and split accross all the threads might make lightmass significantly faster. I would have a pop at it myself if I had the first clue where to start, but this is probably one for the rendering team anyway.
…or ability to choose number of cores, so one can surf/whatever while lightmass is calculating… just a thought… 
Fantastic results from the portal lights.
I see the suggestion here is to use uncompressed lightmaps. Doing that I also found the quality higher, esp. when larger surfaces considered. But using a lof of 512/1024px maps, this seem to facilitate higher memory usage and thus lightmaps mip-mapping.
Which shouldn’t be a problem with 12gb vram of Titan-X, but I couldn’t stop this process by changing all .ini files I found on internet. No matter if I set shadow/lightmap mip-maping to 0/false, or rised value for memory pools, both in project and general folders, etc… it would always mip-map those lightmaps,
which is just visually horrible. Anyone with similar issue got this solved ?
Why Ue4 not use bc6h for lightmaps? Quality should increase significantly.
Like suggested, increase your memory streaming pool. I had the same problem on my gtx 980 4gb. I increased it to 4000 like that : r.streaming.poolsize 4000 (no more mip mapping like crazy)
Never had a problem after that and I usually have 4k textures and 2k lightmaps sometimes!
Really really happy I managed to finish this scene in 59 mins (lighting build time)! I have shadows everywhere The only settings I adjusted was the lighting level scale.
I took an evermotion model and optimized it for Unreal. I managed that lighting/shadow quality in 59 mins because of this thread and community. You guys rock!
Every tile has geometry, walls also have extruded parts, so it wasn’t THAT easy to remove all lightmaps artifacts.
Looks great Phil. However, I found that it’s a bit odd that using smaller value for Static Lighting Level Scale can make the rendering more faster (as long as the other value in Lightmass kept to default, except Indirect Lighting Bounce). Especially because the tooltip says that using smaller values (less than 1) will increase build time greatly. I also found that using 0.4 gives better shadows and faster rendering time than value of 1.
Yes it will increase the build time but compared to the other settings, it’s really not that bad. I left indirect lighting quality to 1, bounces to 10, smoothness to 1 and it’s the defaut baselightmass.ini. I really only used a scale of .4, uncompressed lightmaps. 
My previous version took 16 hours and looked worse with the other settings cranked up. This scene lighting is simple tho, just a skylight with Epic’s HRDI.
Also, by leaving the rest of the settings to default, I was able to raise the resolution of my lightmaps to 1024 to clear all artifacts, something impossible in my previous attempt that took 16 hours with 256x256 lightmaps :-S
@: is this Production lighting or less? If you’re able to achieve this lighting in 1 hours at Production level you won the competition 
This is production lighting yes.
But it’s a big outdoor (mostly) scene, no furniture and small objects that would need huge amount of detailed shadows!!!