This is Marc-Andre, the chief guide at the La Fleche Caves near Otawa. Marc-Andre was one of my three companions during this last exploration and in the photo, Corneile, his wife provides a most interesting backlighting with LED light.
Cavers tend to use a combination of different light sources. The regular Petzyl incandescent lighting can be seen on Marc’s helmet along with some kind of newer carbide lighting above. I regularly use this type of Petzyl lighting as it is waterproof and easily supplied with batteries. Carbide is favoured by traditional and expedition cavers for its vastly superior light. It pools around you in a warm glow and as said by the once famous British caver “Belch”, “It casts no treacherous shadows”. To its disadvantage, some of the carbide lamps can be very temperamental, they require regular cleaning and the fuel, solid carbide is sometimes hard to come by. The general idea is that when mixed with water, carbide releases a flamable gas and this is burnt in front of a reflecting shield for light.
LED provides a pretty intense blue light and it is very conservative with ones power source. I suppose you can say that it is environmentally friendly as no fumes are given off and in a cave such as this one, with wonderfully smooth, tan colored dolostone and domes and chambers of ghost-white calcite deposition, to stain the walls with a carbide burn would be grossly invasive.
For photography, I favour a combination of different lighting. The contrast between warm incandescent and cool fluorescent or blue LED can be very pleasing.