Luoshuang's GPULightmass

Hey @Luoshuang just ran DDU on my drivers and reinstalled, no joy. Any insight into the error I’m getting? Thanks!

Any news about Sparse Volumetric Light Samples on 4.20?

Arghhh I also desperately need them!

Try to make Directional light as stationary.

4.20.1 version has incorrect & Sharp shadow for skylight ! why ?


Should be fixed now. You can download and test again:

Reference: V-Ray for Unreal 4.19, Reinhard tonemapping, exposure 3.0, highlight compression 0.5:

Fixed 4.20.1:

There are still some shape differences, however I believe that’s due to different tonemappers

I have the same problem here since the 4.20.1 Update,


I don’t know why, sometimes it works…
GeForce GTX 970 / Driver Version 398.82

@Luoshuang I just tested on a brand new machine out of the box with 4.20.1 and GPU Lightmass, same error again. :frowning: Delay is set to 6000. I feel better that it isn’t just me though.

Maybe it will be fixed in the update for 4.20.2 build, please ? :o

I’m about to test this out. One question…when I click on the download link, I get 4 zip files. Each with different names. Which on do I use? All of them?

Running into issues: Once I unziped the Extreme file and installed the folders I run my light build and get the following errors before build fails. Thoughts?

Are you using an Nvidia GPU? Are you using the latest drivers?.

I have a Geforce gtx 1080 installed. How do I check for the latest driver updates?

Nvidia Cuda 9.1.84 Driver.

Just did some Tests in the 4.19 Version and it works pretty well! Rendered this small studio apartment:

  • Time: 25 minutes
  • GPU: 1080 Ti OC
  • Num Indirect Lighting Bounces: 10
  • Lighting: Just a SkyLight with a simple white cubemap
  • Lightmaps: Walls/Floor/Ceiling 4096, Windows 2048, Table 512

For some reason (“Failed to send back log file through Swarm!”) my other PC’s stop just right before mapping process.
Seems to be some weird Network/Switch problem because it worked for one build but then failed all the time.

Can it use multiple GPU’s in the same system? (no SLI)

Thanks Luo!

You need to update, that’s pretty old. The question has already been asked in the thread.

I made a script that will automatically download and install GPULightmass on your binary installation folder, perform a batch of checks to avoid issues (like nvidia driver version and TdrDelay), and allow to change GPU bake quality among fast, medium, high, extreme, without the need to restart Unreal.

If it helps someone, just give me a “Like” below.

It’s currently working with the latest engine version (4.24.1). If you need it to work with a previous one, just replace UnrealEngineVersion variable in LightmassConfiguration.bat to the version you need (use only 4.xx notation, do not use 4.xx.yy here).

UPDATE 3/1/2020: Script got updated to 4.24.1

UPDATE 12/11/2018: Now updated to work with 4.21 (Unified Settings). Allows to chage settings on the fly between different BaseLightmap.ini configurations.

Now on GitHub: GitHub - sgeraldes/LightmassConfiguration: LightmassConfiguration is a script made for Unreal Engi

DIRECT DOWNLOAD to the latest version:


  1. unzip to any folder (empty folder is better).
  2. double click the .bat file and follow the instructions

What it does:

  • The script will download GPU lightmass 4.20.2 from the OP into the same folder, backup CPU Lightmass for you, and install GPU on your choosen quality level.
  • It features an undo or “Restore CPU Lightmass” option.
  • On-the-fly switch of GPU Lightmass with UnrealEd running (no need to restart unreal).
  • It works with 4.21, but can easily be adapted for 4.20x and 4.19.x if needed by adjusting a few parameters inside the file (just edit with Notepad and change UnrealVersion variable to 4.20 or 4.19.

What it does not:

  • Brew you some coffee


  • Windows 10 (not tested in earlier versions, may work but no guarantees)
  • Admin privileges

The script has the following features:

  1. Show you the version of Nvidia drivers running (and any other display driver that’s running, i.e.: Intel HD) and warn if not sufficient
  2. Check if you have TDR settings as recommended, IF NOT: the script will ask you to do the changes for you (optional)
  3. Allows changing GPU Lightmass quality settings (fast preview, medium, high-ultra, extreme) without needing to restart unreal.
  4. Backup CPU lightmass for you and give you the option to go restore it later
  5. It will override BaseLightmass.ini on your Unreal folder (it will first backup in the zip archive the version you have and allow to restore at will).
  6. Checks if GPU Lightmass is installed, if not…
  • Download the latest version of GPU Lightmass for you from Luoshuang’s links

  • Download 7Z.exe to quickly backup and perform decompression of the files in the archives

  • Finds the installation directory of Unreal, and unzip the files there according to the quality you select (will prompt you for it)

  1. If UnrealEd is running, the script will disable the option to change GPU and CPU lightmass as it needs to access files that are in use to do so.

Please note: The script will give an error while copying when trying to change the quality settings with Unreal Ed running. That’s perfectly fine, the file is just been copied over to be sure it remains the same. I guess I could just copy GPULightmassKernel.dll instead of the whole bunch, but I just think it works as-is just fine. The copy of a single will fail but GPU Lightmass will work the same.

Also note: the script can’t change from CPU to GPU lightmass while the Unreal Editor is running, so the script will check for that and disable the option accordingly.

The only file that has the changes for quality, and the only file that is in any way different between the different packs, is GPULightmassKernel.dll (I did a binary compare of each file to be sure).


[/SPOILER] [HR][/HR]UPDATE 12/11/2018: New Version 0.3.2. Updated to work with UnrealEd 4.21 (Unified Settings). Allows to chage settings on the fly between different BaseLightmap.ini configurations.
UPDATE 09/23/2018: Version 0.3.1 It now works with UnrealEd 4.20.3 and GPU Lightmass Unified Settings. Also created a menu to change Unified Settings quality choosing from the different presets. Fixed a bug with backup of CPU Lightmass that may not keep folder structure in the zip archive.
UPDATE 09/22/2018: It currently works with up-to 4.20.2 as binary distributions for GPU Lightmass 4.20.3 are not available. The installer doesn’t work either with Unified Settings, so I’m working on a new installer to work exclusively with it.
UPDATE 08/23/2018 v0.2: Modified to allow easier updates of the engine. Fixed some bugs. better detection of some parameters and added a fail-safe in case it fails.TDR settings now in decimal instead of hexa .
UPDATE 08/23/2018 v0.2.1: The script now actually checks for driver version and warns the user if the driver does not meet the requirement.


I have the same issue. I tried on a swarm with 4 workstations, they all worked in parallel until the last bit and failed to sync. The single workstation took the same time to render as when it was alone. I was under the impression it was some network/firewall issue also but they all communicate properly.

today 4.20.2 is update …lol

I just had a look at the log file and it says: “A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)”

UPDATE: After using “Verify” in the Epic Games Launcher (resets to CPU) and immigrating the GPU files again its working now!
I CAN’T BELIEVE HOW FAST IT IS!! I hope it will still be working after a restart of UE or some other action that might mess it up again…