An iPad camera generally won’t record usable video in a completely dark room unless there is some light available. The lowest-cost thing to try is a night-video app, but results may be limited and compatibility with iPad should be checked first.

A more reliable solution is a camera designed for low-light/night use, such as a baby monitor or security camera with built-in night vision (typically infrared). These are meant to record in darkness and often include useful features like motion detection and remote viewing from a tablet.

So in practice: if you need dependable results in a dark room, use a night-vision baby/security camera rather than relying on the iPad alone.