How to render under lamp light fast?

James

I find rendering under sunlight is faster then under lamp llight.
Why ?
Is there a way to make it as fast?

Richard Haseltine

Sunlight, whether an HDR envirnment or the Sun/Sky system, is sending light from multiple directions (more-or-less every direction) and may well have few obstacles to the light, or things for light to bounce off. As a result each pixel of the image is probably going to get close to its final value very quickly, and so the default behaviour of stopping when the target percentage of the image is "converged" is easily achieved. By contrast a lamp-lit scene has localised light sources, and probably has lots of items blocking light and allowing light to boune off. As a result some surfaces will occasionally be hit by a light path bouncing from a strong source and sometimes not hit by anything, so it is going to take a relatively long time for pixels to settle close to the final values and so the render may keep grinding away.