Summary:

Get yourself a small red LED keychain light.

The Good:

• Very dim so you won't wake up others when you are digging through your bag in the night.
• Since it's red you won't be blind when you turn it off.
• Being a keychain light and cheap, you can attach them to the strap of every bag and jacket zipper you have so you always have 'some' form of light with you. And with redundancy like that you won't run out of batteries any time soon.

The Bad:

• Using a non rechargable watch battery, the life won't go on forever if you do long term camping.

Details:

There's really not much to say other than, the last thing you want to do is turn on your lantern or welding-goggle-required flashlight, when all you are trying to do is find your water bottle, or not trip over tent spikes while trying to take a leak at at 3am and you don't want to draw attention or wake others with a bright light. 

Keep as dim as you can, not bright as you can.  But make sure you have the power to go bright as needed for the situation.