Point lights shine up onto the ceiling as well as down into the room. If they are in fixtures, they shine onto the fixture surface.

These surfaces that are close obey the inverse square law, which for point sources means that the intensity not only decreases with increasing distance, but also increases with decreasing distance - squared.

So - imagine you set the light to 80% intensity - that's the luminance at 1 Poser Native Unit, or roughly 103 inches (or 96 if you still believe in the Poser 5 measurement system. No matter...) Let's keep the math simple and call it 100 inches.

At 50 inches, the intensity is 4x 80% = 320%.

At 25 inches, the intensity is 16x 80% = 1280%

At 10 inches, the intensity is 100x 80% = 8000% (Already pretty intense but we're not done)

At 2 inches, the intensity is 2500x * 80% = 200,000% !!!!!

So - if you have those point lights 2 inches away from the ceiling, parts of the ceiling are brighter than the arc of a welding torch.

Now - part 2:

IDL sends out rays to sample the lighting from the world and decide what light is reaching every point in the scene.

It can't send out as many rays as real life, so it sends out anywhere from a couple dozen to a couple thousand from each sample area, depending on your IDL quality settings.

Now you have these few ultra hot spots on the ceiling, and the rest is much darker. Most of the time, none of your few-dozen sample rays hit a hot spot and it looks normal. Once in a while, a single ray hits one of these 2500 x brighter spots and it overwhelms the other samples - you got a hot spot on the wall.

Solution: (Assuming you don't accept the get-another-renderer solution)

1. Use spotlights instead of point lights so they only shine down, not up. Requires some tweaking as the falloff is not set up as mimicing real lights by default. I'm talking about the angular falloff here. Real spotlights have some angular falloff, but not like Poser default spot lights do.

2. Move the point lights away from the ceiling a bit more.

3. Put something black between the point lights and the ceiling (just in the places that are really close.) If you happen to "see" these objects because they are in the cameras view, then make them invisible to camera. IDL will "see" them, but the camera won't.

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