These two cool videos show the beneficial effect of lighting (in this case IR light, which explains the monochrome image) on the bitrate of IP cameras. Of course this applies equally to encoders and anything else, like most DVRs, that compress based on the difference between successive frames, typically MPEG-4 and H.264.
The bitrate drops from over 2000 Kbps to 364 Kbps on high quality settings and 30Kbps to 13Kbps on lowest quality. Imagine the storage and bandwidth savings on a Megapixel camera at night.
Quite incredible and never ceases to surprise people, but very easily for you to duplicate.
Feel free to watch the 1 minute videos at http://ow.ly/jXw5 and http://ow.ly/jXwx