用于某个区域内光源的光线数量。允许准确的柔和阴影。
This is the maximum number of rays to trace to any light with an area. Larger lights will require more rays to produce a noise-free output. The default value works with the majority of Scene setups, but you should increase this value if you observe noise. It can have a significant impact on performance, and for Scenes with lots of area lights, halving this value halves the baking time.