I'm in Sanctuary, and suddenly I have a flashlight-looking icon on the right side of my screen, even in the daytime. I'm concerned only that this is "using up" something I need -- can someone tell me what it is and whether I need to turn it off?

It indicates your pip-boy light is active, hold down B or O or your respective button to turn it off again. Button should be in the options menu if you're unsure.

Your pip-boy light?

Hold tab/Square/X

edit: Oh, is it O/B?

Piplight. On PC, hold down TAB for 2 seconds to toggle it.

It's B for me, which is the equivalent for PS controllers, O.

Thanks, everybody. Takes a while to learn the controls.