Shadows in the darkness?

[Hatez]

When I was watching lastnight, I noticed that when they had the lights off - there were shadows of the duvets cast upon the beds of the other housemates. It was with the night vision cam on, and as I understand - when the lights are off in the bedrooms you cant see a thing.
So, if it's dark in there - where do the shadows come from?
Next time the lights are off, see for yourself - it's weird.

[Hatez]

This is really doing my head in now - theyre in bed, lights off - but the night cams are still showing up shadows, and shadows need light to exist.
*Can't figure this one out*

[Hatez]

http://www.thisisbigbrother.com/gallery/displayimage.php?album=42&pos=19.
I Keep hearing how dark the rooms are at night, and I know that those cameras wont work when there's light, they just show a bright white picture.
Take a look at that place, it shows the shadows.

[James]

These types of night-vision cameras work by enhancing the small amount of light present in a dark room; they wouldn't work in absolute darkness.

My guess is that the light is enough to cast shadows which show up when enhanced.