Lumen GI + Skylight = Glowing Lacrimal Fluid

Looks like Lumen’s GI doesn’t play nice with Metahuman’s default lacrimal fluid material when illuminated with a skylight. Below you’ll see that without the skylight, and without Lumen GI, there is no issue. This can obviously be reduced by lowering the opacity of the lacrimal fluid, but the default setting looks ridiculous.

Considering that UE5 + Lumen GI will likely be the showcase configuration for Metahuman in the future, this default probably needs some tuning. Below you’ll find some comparisons taken from the 3rd person example map.

(L) Lacrimal Fluid Opacity 0.0003 (R) Default Opacity 0.04

(L) Lumen GI with Skylight (M) Lumen GI Skylight Hidden (R) Screen Space GI with Skylight