My first headlamp I used had an ordinary flashlight bulb so when the battery were dying the light would drop off quickly. I was connecting the primaries for transformer one evening in the concrete vault off of a 480 volt distribution system. Although the distribution system was shut down for this, It was "interesting uncomfortable" to be in there when the batteries went dead. I gingerly had to climb out of there in total darkness.
Lesson to carry a spare?
Spelunkers always carry 3 sources of light- and they won't even consider it a source of light unless you've got spare bulbs and batteries for it.
Personally, I don't like to be
anywhere without at least a small 1xAAA LED light in my pocket, night or day. I had a camping watch once, had a tiny little LED light on it; I hated to use it because it would drain the button cell and the watch was ugly as hell, but man, that thing saved my ass on 3 separate occassions!
