Question: I want to take some video of a friend with a motor disorder while he is sleeping. We are doing this to help get information about what happens while he sleeps. 

I have a tripod and set up my iPad to video tape. But as soon as I turned off the light, the iPad could record nothing. I thought the iPad camera mode might have some way to brighten the image so that I could record, but nothing happened. 

What is the least costly way to film my friend in the dark?

Answer: 
If trying other cards has not worked ([as indicated in comments](https://photo.stackexchange.com/q/81698/75526#comment140065_81698)), then the problem is not the card, it's the camera. You will need to get it repaired or at very least disassembled and cleaned by a specialist.
It might be the card, it might be the camera. Check for dirty contacts on both. If that doesn't help, try the card in a card reader attached to a computer, try a different card in the camera. Now you know where the problem lies, yes? If it's the card (and the pictures on it matter) there is free software that MIGHT be able to retrieve them.