Top image: Evermotion
Disclaimer: remember that this solution is unofficial and should not be used in your important projects. Installing GPU Lightmap files is very easy, but it overwrites Unreal Engine settings and it should be done on machine / software version that is not used in your current productions.
What is it? It is GPU lightmap baker, which is generally up to 10 times faster than baking light maps by nowadays CPUs! It means that high quality Global Illumination for your interiors / exteriors is now easier and faster to achieve, installation is very fast and GPU Lightmap baker does not require tweaking any settings - all are hardcoded now (which will change in the future). How fast can it bake? A scene having 30M triangles and 150 1K lightmaps requires 7GB video memory and approximately 3hrs to bake on a GTX1080.
- Binary installation: download here - the easiest way to install GPU Light Mapper. Just unzip the archive and merge "Engine" folder with your installed Unreal Engine 4.19 version "Engine" folder. This installation overwrites your BaseLightmass.ini so you want to back it up if you have modified its parameters.
- Source Installation: download here
Image courtesy of Makigirl
- Written in CUDA so NVIDIA only
- Supports all 4 standard lights (point, spot, directional and sky)
- However stationary skylight is not supported so if you have one in your scene it will still be baked since it is treated as a static one
- Advanced lighting features such as soft shadows (SourceLength and SourceRadius) and IES are not respected when calculating indirect lighting. However you may still see some effect of them since their direct lighting is calculated on CPU
- Supports baking of standard surface lightmaps, volumetric lightmaps (also with faster voxelization), and sparse volume lighting samples
- Lightmass parameters and quality settings specified in the editor are ignored except for Num Indirect Lighting Bounces
- Current the number of samples (quality settings) is hardcoded in the program and you cannot change it since I haven't found an reliable way to expose them to the user
- AO Mask generation is not supported
- Since adaptively placing more samples around corners (known as Retrace in vray) hasn't been implemented you may see sploches.
Read more and discuss this topic on Unreal Engine Forum!