1 cove light, 6 passes. Rendering time 22 seconds
Cove Lighting refers to lighting in a suspended ceiling where the lighting itself points up and is then reflected by the ceiling into the scene.
Here is a model with cove lighting after just 6 rendering passes. The model has a single light applied to the entire upward facing surface on top of the recessed area of the ceiling. The way the nXt engine works, random points in the single light are sampled for each lighting pass, so, of course, after only 6 passes the lighting effect is pretty ragged.
After 30 passes the lighting in the room is more balanced, but still the lighting above the ceiling shows the effects of the individual lights. This will improve with additional rendering passes.
After 1,000 passes, (this probably looked OK after a few hundred passes, but I let it run for 1,000), the lighting is fairly smooth.
However, if there had been other lights in the room then it may have taken too long to process the cove light for this many passes. There are two potential solutions for this.
1. Break the cove light up into multiple lights - for break the lighting surface into multiple faces.
2. Tell the renderer to process the area light multiple times per pass. (Not available yet). This would be easier to implement, and we are hoping to modify the nXt engine so that we can make this a parameter for area lights.
For this next image, I divided the cove light into 30 separate faces. Each one is treated as a separate light. It converged much better after 6 passes, but also takes longer to render - because there are more lights per pass. The value of this technique would apply when there are other lights in the model which do not need as many samples as the cove light.
