Hi
I rendered a bathroom where there is a mirror. I use cycles and an area light. When rendering, the light appears in the mirror as a white plane, not in the ‘not-reflected’ world… curiously, if I uncheck Multiple importance that white plane dissapears… but I get too much noise. Is there a way to avoid that white plane?
Ok, sorry… I’ve just discovered I have to unselect glossy in the Ray visibility!
I’m not a cycles expert, but wouldn’t it be more beneficial to uncheck “camera”? I assume the main problem for you is the visibility of the source. Not it’s effect.
No, because lamp objects are invisible to the camera anyway and the camera ray tag no longer applies after said ray has bounced.
Good to know, thanks. 
I use mesh sources more often than lamps. Usually in a simple capacity.