Can you somehow turn off Nikon D90 video's flickering exposure?

Every time I try to shoot some HD video with my Nikon D90 it seems to automatically adjust the exposure depending on the darkness of the shot. I'll film out a window where it's bright and it looks fine, but as soon as I shift over to a dark area the exposure flickers up and up until you can see detail in the shadow. It's helpful and all, but it just looks weird when the exposure is changing in the middle of a shot. I wanna just have one exposure regardless of whether or not you can see anything so it looks cleaner. I tried putting it on manual, and tried looking around the settings, but nothing. Any suggestions?

Two things. One video cameras don't "film" they record. Film is in Hollywood.

Second, one exposure won't work. When you point the camera outside the aperture closes down just like your eye does. When you point it inside where there's not nearly as much, just like your eye, the aperture adjusts to that light. If it didn't you wouldn't see anything inside - get the drift?

Most, if not all, still cameras that also do video, everything goes to full auto in video.

Exposure can be locked. See page 50 of your manual.