Lights Per Pass
Lights per pass determines how many lights will be processed per rendering pass.
The default is 33%. You can change the percentage or enter a specific number so that more (or fewer) lights are processed per pass. (Of course, each rendering pass will take longer with more lights, and you will need more rendering passes with fewer lights.)
Area lights - such as a rectangular light are rendered by treating random points on the area as a light source. With a lower lights per pass it takes much longer for the are light to have the desired effect. Increasing the lights per pass and/or allowing more rendering passes will make these look more realistic. (In either case, each area light will process no more than one light per pass.)
- See: Special_Options_Tab