Canon T1i - Banding In Video

I am using the T1i on a microscope, so the light level is pretty low, compared to daylight, however, it's enough to do the job. Almost from the first day, I have been seeing banding in videos, while stills show no banding whatever. Even shooting stills while shooting video, the video is banded and the stills are not.

I use EOS Utility to shoot stills or video, with live view.

Now, one time, awhile back, I noticed, after shooting, editing and uploading a video to YouTube, I had a few movies in a row that had no banding, but didn't notice it till a day later and had forgotten what I might have done different.

So, my question is, what causes it, and how do I stop it in the future?

Here is a recent video, edited in Premiere Pro CS5. And a thread with some stills shot while the camera was recording the video, no bands.

Thanks for any help.

For the record, the banding in T1i video mode was due to too much brightness hitting the sensor. That was the last thing that I would have expected, mounted on a microscope. Yes, the light, when cranked up to max, can hurt your eyes, but it just never connected that it could overwhelm the sensor.

Anyway, problem solved. In my scope at east, as long as I keep it under 8v, about 2/3 max, there is no banding.

Here is a 3 minute video showing the problem, and the cure.