Currently, emitters are single-sided. If a ray hits some back-facing emitters, its intersection point may be slightly in front of the emitter. Consequently, if the emitter's material is double-sided and picks a sample direction on the same hemisphere with V, we will intersect ourself and this time causing light leaks. The amount of leaking light is tiny but visible. This scene demonstrate the issue:
Currently, emitters are single-sided. If a ray hits some back-facing emitters, its intersection point may be slightly in front of the emitter. Consequently, if the emitter's material is double-sided and picks a sample direction on the same hemisphere with V, we will intersect ourself and this time causing light leaks. The amount of leaking light is tiny but visible. This scene demonstrate the issue: