Hi All,
I was wondering if it is possible to turn off the lighting that’s being cast by emissive materials.
Reason why I would like to do this is to optimise for lower end PCs while creating particles.
I would also like more control over the light and its color that’s being cast by the particles.
Thank you all 
I am not fully sure if it is possible or just as simple as pressing a checkbox. There are some post process and shader tricks you can use, but they will most likely not give you a super good result.
I found this, so please consider trying the below:
Turning on or off Emissive Influence on the World
In some cases, you might want to or not want to have the Emissive Material cast lighting into the world. To enable or disable this feature, follow the following steps.
- To accomplish this, first select the mesh that you do not want to cast light from the Emissive in the world.
- Then in the Details panel, under the Lighting section, check the box that says Use Emissive for Static Lighting by using the Left Mouse Button and clicking on it.
By default, Use Emissive for Static Lighting is disabled on all meshes that you place inside of the world. If you want to use it, you will always have to enable it.
Thank you for your reply,
I tested this out before and this option does not seem to work or change anything to my scene/light. Also the fact that I’m searching for a solution is so that I could use it in particles, which will be dynamic and having a static light cast out of the particle, would come over as quite weird.
The only way to do this is to disable screen traces.
Lumen relies on screen traces as its first method for generating GI, and it will always pick up what is visible on the screen.
In order to prevent a mesh from rendering any GI at all, you need to disable screen traces and set the mesh so that it is ignored by the Lumen scene (does not affect distance field lighting, not visible in raytracing)
This is going to create different problems though, as the screen traces in Lumen help correct errors in the Lumen scene, such as light leaking and picking up details that the Lumen scene couldn’t capture.
The command for disabling screen traces is: r.Lumen.ScreenProbeGather.ScreenTraces 0
@Arkiras is totally correct here, there are a handful of threads on this topic that have all come to the same conclusion.
Although the main goal of optimizing by disabling the emissive lighting propagation is misguided, as per Epic’s statement emissive light in Lumen is free from a performance perspective.
More control over this would be nice for artistic reasons, but don’t expect to gain any performance if they ever implement it.
Thank you for your replies.
After researching some more, I do believe it is impossible to do this per mesh and that it’s only possible for the whole scene at once.
Another solution would be to work with a post pro that encapsulates the player, but I feel like that is super unoptimised and inefficient.
Also double checked how heavy it is to run particles with the emissive light and it seems that the cost is indeed very low (but the cost of activating Lumen for GI is roughly around 40fps for my workstation)
So in short, It’ll all depend on the project I’m working with and waiting to see if Epic Games will give us the option to exclude meshes/particles from GI.
