You are going to get a 100 different opinions lol.
I "think" Tim (webmaster) has one mounted on his lid and if he does he will be the best person to ask (He is at Knowlsey Safari Park today the poor sod).
Light is obviously crucial underground and video cameras won't work without it (this is not as obvious as it seems).
I have tried many video cameras and they were virtually all very poor in low light conditions (even one I tried out with a purchase price of £1600).
I found a small, Nth generation video/photo camera which can be bought on Ebay which seemed to handle the low light well but, sadly, they die very easily underground and it is not HD.
See if Tim picks up on this thread before you buy one (I know Tim also has stupidly strong bright lights too)
Ian