Those are oil lamps on their heads, not candles. They also used carbide lamps. Don't feel too badly for the horses (usually mules), my dad said they typically worked shorter shifts. He worked in the mines at about this same era as a boy, from around 1910 to 1955.

These lads and their pony are being photographed near the bottom of the shaft - they have room to stand up! The guys who cut the coal (hewers) would work on their knees or lying on their hips, swinging pickaxes for hour after hour, and breathing in all sorts of dust. Don't ever let anyone romanticise coalmining. I come from near Newcastle, and I know that the earth under my feet contains the bones of centuries of colliers. Horrible!

I think this photo will give me nightmares. Just creeps me out.

Those are candles on their heads? Send the expendable ones down first!

[Gasoline or oil headlamps with open flames. More here. - Dave]

About to be immortalized on film, and the one on the left shuts his eyes. It looks like he led a bit of a miserable life; shame he couldn't even get the photo.

Poor horse, too, of course.

[Both his eyes are open -- and closed -- in this time exposure. - Dave]