Using Lumen, trying to make a simulation with an array of quite small, movable meshes (maybe 2x1x2 cm) emitting light using emissive materials.
They behave like if I was using screenspace, i.e. when off screen they do not contribute to GI at all.
In the same scene, I can add for instance a basic movable cube (which is 50x50x50 cm if I remember correctly) and it does throw light even if it is off screen. So Lumen is working and active.
So, this leads me to believing that there is some lower limit for how small objects that cast light off screen can be. Is that so?
And if so, can this limit be altered with some setting?
Hate to be the bearer of bad news but you really can’t use Lumen this way (yet)
If you are using hardware raytracing with Lumen then in the actor properties for the mesh, you can set “Emissive Light Source” to true and it will help prevent the mesh from getting removed from the Lumen scene when it gets too small. This can also help with software raytracing, but not nearly as much.
But the results will be noisy, to some extent this can be mitigated by increasing the final gather quality (in the post process volume) but in general… as I said; You can’t really use small emissives with Lumen right now and expect good results.
Hey there @PatMag68! As @Arkiras had finished saying before I did, Lumen doesn’t gather from tiny objects as raytracing cannot feasibly hit every square inch of anything without incredible overhead. You can however try and get some better reactions by following what Arkiras said, as well as increasing the final gather and lumen scene quality. That said it will get exponentially more expensive to do so, so be very wary!
A thread with my answer on how to change some of those settings:
