Why does a bright video feed send more data than a dark one? I've been watching the feed from a webcam (Foscam 8910).  When the scene is bright (lit with sunshine) the video feed is approx. 350 kBytes/sec.  When I view the same scene lit very dully with just a dim bulb, the feed comes at approx. 50 kBytes/sec.

As I understand it, the video feed only transmits the changes between frames.  Once the image has been transmitting for a few seconds, and there is no change whatsoever in the scene, the feed should settle down.  

Why is there a seven fold difference in network traffic between light and dark scenes?  Shouldn't they be identical?
Our eyes and brains are more sensitive to data in the bright areas so compression schemes generally throw out more of the data in the dark areas. If the video is mostly dark, then it compresses very well because they can throw out more data and you don't notice. But when it's bright (assuming it's not overexposed), less data can be crunched down without you noticing it.