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You then probably want to seperate the emmission to just sit at 1, illuminate and do absolutly nothing else. Pr default emission cast a ton of noise as you noted.
You should be able to disable the diffuse reflection contribution on the mesh, so it only emits lights and contributes with exactly 0 rays being thrown around.
in max my hook is visible_to_diffuse_reflections = off
Via a property modifier attached to the light, you may find a simular option set in your host.
This is the "mesh light shader" that MtoA outputs:
input1 of the aiMultiply is the light color, and input2 is a intensity multiplier