Dark video

I know a few years a good the best camera for filming inside was one with a single large chip. Most cameras have multiple smallish ones apparently to give you good colour quality.
You need light to reflect the wavelength of a colour, so if there is no light the CCJ's (digital equivalent to light sensitive grains) have difficulty deciding what to do or what shade to give, (the absence of colour is not a colour,) giving you a grainy effect. You can increase the amount of light into a camera in low conditions ie shutter speed but this may give you blurred photos.