I’m trying to make lumen work with my artstyle but the solutions I’ve searched to fix the lumen flickering are with using TSR anti aliasing. Unfortunately anti aliasing doesn’t work with my pixelated artstyle. (I’m using Pixel Tools by Turbomorsh and substrate toon shader in 5.8)
I’ve been researching this for the past 2 days trying to make lumen not have artifacts or looking for alternatives. I tried baked lighting but for some unholy reason it keeps getting stuck at 0% and crashing. (Tried troubleshooting but no solution that worked came up)
Now I’m back to trying to find a solution for lumen, adjusting quality settings and googling and asking AI. I desperately need lighting expert guidance right now.
After following this video, I noticed a significant improvement with the command “r.Lumen.ScreenProbeGather.ShortRangeAO 0”.
I asked Epic’s AI assistant to explain what’s happening:
"By disabling Short-Range Ambient Occlusion (SRAO), you have removed a specific sub-pass of Lumen designed to handle very fine, high-frequency contact shadows.
Here is the technical breakdown of why this fixed your flickering and what you are sacrificing by turning it off:
1. What is Short-Range AO?
Lumen splits indirect lighting into two parts:
Global/Long-Range: The broad light bounces that fill a room.
Short-Range (SRAO): The tiny shadows in corners, cracks, and where a character’s feet touch a colored platform.
Because tracing rays for tiny details is extremely expensive, Unreal Engine uses a very low number of rays for this pass. To make these few rays look smooth, the engine relies heavily on Temporal Accumulation (Anti-Aliasing).
2. Why it causes “Flickering” without AA
When you use a pixelation tool and disable AA, you are viewing the “raw” output of those few rays.
The Sampling Gap: For every pixel, SRAO might only be sending 1 or 2 rays. These rays hit different spots every frame due to a process called Jittering.
The Noise: Frame A might hit a shadow, while Frame B misses it. Without AA to blend Frame A and B together, that single pixel jumps between “Dark” and “Light” at 60 frames per second.
The Pixelation Factor: Your pixelation tool takes that one flickering pixel and scales it up to a 4x4 or 8x8 block of pixels. This turns a tiny bit of sub-pixel noise into a massive, shimmering block of light/dark, which is the “flicker” you observed.
3. What happens when you set it to 0?
Setting r.Lumen.ScreenProbeGather.ShortRangeAO 0 tells the engine to eliminate that high-frequency trace entirely.
Stability: The flickering stops because you are no longer asking the engine to calculate a pass that it cannot properly denoise without AA.
Visual Trade-off: You will lose the “micro-shadows” that ground objects. Your character might look like they are “floating” slightly on the colored platform because the sharp contact shadow where the feet meet the floor is gone.
4. How to get the quality back safely
If you find the scene looks too “flat” after this change, you can replace the lost SRAO with more stable, non-temporal techniques that don’t flicker without AA:
Distance Field Ambient Occlusion (DFAO): In your Post Process Volume, ensure Ambient Occlusion is enabled. DFAO uses the Global Distance Field to create soft shadows. It is much more spatially stable and does not flicker like Lumen’s SRAO.
Screen Space Ambient Occlusion (SSAO): A classic technique. It’s less accurate but very stable.
Increase Spatial Filtering: If you want to try re-enabling SRAO but with less noise, try: r.Lumen.ScreenProbeGather.SpatialFilterNumPasses 4 This tells the GPU to blur the noise across neighboring pixels in a single frame (Spatial) rather than across time (Temporal).
Summary
By setting that value to 0, you have eliminated the specific part of Lumen that is most dependent on Anti-Aliasing. For a pixelated, non-AA aesthetic, this is a very common and effective optimization, as the resolution of your “pixels” is usually too low to represent that micro-occlusion detail anyway."