I take it you've read the docs?
You need to use EntityFX ent,2 to enable vertex colors on the target mesh before you can see any results.
Since V1.83 the default vertex color for primitives is 255,255,255 and not 0,0,0, so for LightMesh to effect primitives as it did before, you will first need to reset the vertex colors to 0,0,0. You can do this using LightMesh mesh,-255,-255,-255.
You need to use EntityFX ent,2 to enable vertex colors on the target mesh before you can see any results.
Since V1.83 the default vertex color for primitives is 255,255,255 and not 0,0,0, so for LightMesh to effect primitives as it did before, you will first need to reset the vertex colors to 0,0,0. You can do this using LightMesh mesh,-255,-255,-255.