My emissive object changes color/brightness quickly. However, the bounce lighting from the emissive fades over roughly a half second or so. Bounce from normal (Point/rect/etc.) lights in the same scene do not fade.
I know emissives render a little differently, but what causes this, and can I prevent it?
See this gif. Particularly noticeable on the blue to green transition:
The global illumination from lumen is accumulation based and cached. But what you can do is reduce the update speed when you change something with the lighting and then set it back. I’ll have to look up the console command again.
Thanks! But wouldn’t Lumen be specifically for UE5?
Oh, I saw emissive bounce in the title and assumed lumen, could still be SSR and or SSGI which also combined samples over time.
Thank you! It was indeed SSGI.
Changing some of the settings did speed this up.
Reducing the quality (aka reducing the bounce count) with r.SSGI.Quality [0-4] does speed it up slightly. The biggest improvement was with r.SSGI.HalfRes, although it does produce a lot of artifacts. Others can check the SSGI documentation for more.
In my case, my project is very small, so I’ll probably just disable SSGI and just fake it with actual lights.
Thanks again.
You could also probably visually mask it more with how you transition between colors in the material as well. Physical lights do take time to warm up and transition colors.
Very true, that’s good advice. Although in this case I’m attempting to match the capabilities of specific real-world LEDs, which can indeed snap immediately between colors & brightnesses.
But if anyone else runs into this and has the creative freedom, a slight fade is typically more natural anyway.