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The Petzl Zipka Plus is a great little headlight.
The minimalist retractable headband makes it very easy to carry. Have it with me every day at work as you never know when you'll need hands free...

Plastic soft drink bottle, couple inches water, fold in half, add small pieces of carbide, firmly screw lid on. Throw and wait.

Carbide and water mix = acetylene. Increased pressure + heat in...

The modern carbide lights put out a different kind of light to the old ones.
Sadly mostly overtaken by LEDs for caving. Light lasts longer, doesn't go out in the wet and easier to carry replacement...