every light - except the Sun - is a mesh light, like a reallife softbox. LuxRender handles them with ease, but more of them will introduce a bit more rendertime. Even in a reallife studio, 4 is quite a lot, but not too many.

The main point is that you have to balance the light strength (output watts) with iso / shutterspeed / f-stop. Given the latter, you might just need more of the first so move the light output sliders for 1 to 10 to ?? or raise the shuttertime instead (your model won't move anyway).

The baseline: Render (virtual film) grain means low lighting levels means longer render (virtual exposure) time. LuxRender works like a camera.

My way of works: in my first attempt I (sort of) replace my model by three balls: a 75%white, 50% white and a 25% white. Then I establish all the LuxRender (or Octane) lighting / speed / etc settings in a small image, such that the final saved result measures about 75/50/25% in Photoshop as well. From the statistics I can estimate how long it will take for a final high quality large scale result.

All the best.

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Usually I'm wrong. But to be effective and efficient, I don't need to be correct or accurate.

visit www.aRtBeeWeb.nl (works) or Missing Manuals (tutorials & reviews) - both need an update though