Hey everyone,
i postet the problem already here in the element chat, but for anyone who encounters the same issue, a forum question makes probably more sense.
In general, this Issue only happens with LightSpots [Stride.Light.Lighttypes] used in SpotLight [Stride.Lights] and ProjectorLight [Stride.Lights]. The dots get amplified when the PostFX Bloom and/or LightStreaks are used.
After some investigations, @Sebl and I figured out that the visibility of these black dots/fireflies appear when the inner/outer angle from the LightSpot is too narrow and also not facing the camera. It is not always visible, but in many angles and appear on any opaque material. When the camera is looking through a glass material (SpecularModel is set to Kelemen) you can also see the dots.
@Tebjan mentioned that the shadow maps might be the root of this issue. For opaque materials is this true. If the filter from the LightStandardShadowMap is set to Null, the black dots disappear. For the glass material this has no effect, the only workaround is not to use the Kelemen SpecularModel.
I hope this testpatch can help finding a solution.
Thx