Multiple Graphics Cards

Copied from the old Lightact Answerhub.


What is the behavior with multiple graphics cards in the same machine? Is the GPU for Lightact rendering selectable?

Thank you again.

Hi Jason,

I wouldn’t know. We haven’t done any tests yet although we talked about it some time ago. Inside Lightact there is, at the moment, no select GPU feature.

If you perform any tests, feel free to let us know your findings.


By curiosity and as I’m new to this forum and product, does anyone has successfully used Lightact with multiple GPU. Like my unreal runs on one GPU and Lighttact running on another? Any advancement or roadmad in that direction. The reason why I ask is sometime I need all the power I can from one GPU, or I might have a very large Mosaic display (using nVidia Quadro) using sync card and 2 to 4 connected GPUS…


Hello Remus,

and welcome to our Answerhub!

We haven’t done any tests on multi GPU systems yet and although I believe some of our users have, I don’t know what were their results and if it worked at all.

However, as far as I know, the performance might not be as much better as you might hope. The reason might be that the shared texture would probably need to be copied between both GPUs and as they are usually quite large this would take some time.

Our development efforts are focused on multi server solutions that would work well with Unreal’s nDisplay. I’m happy to say that it’s going quite well, so in Lightact v3.2.2 you’ll be able to have several machines working in-sync on the same Lightact and Unreal projects.

I hope this helps!

Best regards,

1 Like

A bit late, but we’ve done some tests with this. Using NVidia Control Panel it is possible to choose on which GPU LightAct will run.

More information about it here:


A related question – is there any additional setup needed if I want to use the video outputs on 2 graphics cards for different video outputs from LightAct? I will be using 7x 4K outputs for an installation, but each graphics card in the PC running LightAct will have 4 outputs.


Hi Scott,

You might want to have a look at multiple GPU post by @John .


Hi Mitja,

Thanks – I took a look at John’s post. I think my application is much simpler, actually. I have 7 individual mp4 video files, each of which comes in with an individual Video Reader node. Each video is rendered to a separate canvas (x7). Each canvas is the source for an individual video screen (7x). Then, I am hoping I will be able to map each video screen’s output to a separate GPU output (7x).

7x everything! :slight_smile: On the display side, there’s no projection mapping, no warping or blending, just 7 huge video screens. In my understanding, this would not require mosaic or a video splitter, since we’re handling each video individually rather than as one large output texture that needs to be distributed among multiple displays.

I guess a simpler way to ask the question: in the Video Output panel, will LightAct automatically discover all of the GPU outputs on two GPUs in one PC? Will I be able to map each video screen to one of the outputs on either of the GPUs? If not, is there any way you could imagine making this application work? We are using 2x RTX A6000s, so will have a total of 8x GPU outputs, though we’ll only use 7.

Thanks as always!

A quick follow-up – I was able to do a test with our production PC today, and LightAct was able to detect and output video to all 7 outputs from our 2 GPUs! No special setup required as far as I could tell. Windows was set up with 8 display outputs, all set to “extend display”. One was an HD monitor for the UI, and the other 7 will be in the exhibition environment.

So as far as I can tell, this application works natively in LightAct! Very exciting.

Long delayed followup on this thread. I have continued working on the setup for this exhibition, and we’ve discovered that if we run it as I intended – 7x individual outputs on 2 GPUs – the frame rate drops dramatically. The solution is to use Nvidia Mosaic, set up as a single 1x7 output. Huge thanks to @meetya and @John for their help on this.

See discussion here for more information: FPS drop when Video Output is enabled - #14 by smsmith_CM

1 Like