I've been working on an animation, for anyone who has the Maya fundamentals book, i'm rendering my completed spooky house scene. Anyhow, i'm rendering out to tiff, there's 600 frames but having probs with lights. A few times during the animation, the lights just dim to where the scene is barely viewable then after a few frames they are back to normal levels. I have no idea why this is happening, anyone else? I'm attaching two consecutive frames.

I've also noticed the file sizes of the dimmed images are about 85% less than the the images that are rendered correctly. I won't be rendering this scene again, it's taken 16 hours with 2 processors but i'd really appreciate any help for future projects.