It's hard to say what the problem might be. With the default Iray settings (Tone Mapping) a light at 500,000 lumens should give a good amount of illumination. The only thing I can think of that might be causing the problem would be if your light is hidden inside or behind a bit of geometry that isn't transparent (maybe the point emitter is just barely inside the wall, or just barley inside a light fixture). Try moving it to the middle of the room where there definitely isn't anything in the scene to obstruct the light and see if it works then.

Sorry, but that's all I can think of right now.

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