I’ve just ran some tests and discovered that “use emissive for static light” *will not produce light *if unless the mesh has cast shadow enabled. Seems counter-intuitive, as many times I like to have light source meshes not cast shadows so lights can be placed inside without being obstructed. It seems that lights are not blocked by one sided meshes, so perhaps that is a moot strategy, anyway. Will leave cast shadows enabled from now on, for emissive material meshes.
Also, sadly, it seems like this functionality only works for simple meshes… (not something which has multiple parts spread apart, and complex geo behaves erratically–crevices get more emissive response than the flat planes, etc.). Would only expect it to perform properly on cubes, planes (as a cheaper form of the rectLight, cones, spheres, etc.