As a sadly put away all my camping gear for the winter I came across my old lantern, and it occured to me I have no idea how the the mantles work. For those who don’t know,it’s have a little netting, sort of cheesecloth like, hanging in the lamp. When you light it, the mantle starts glowing with a strong white light (and the damn thing will always break on the way home after :(). But what is the mantle doing? Is it mixing the propane and air to the most efficient proportions, or what.
The heat from the burning gas makes the ash of the mantle actually glow incandescent the exact same way a metal filament in a light bulb does.
Not exactly the same as normal “incandescence” or blackbody glow. Lantern mantel light is called “thermoluminescent.” The lantern flame is very dim, but the hot thorium oxide glows fiercely blue-white. Heat a piece of metal to the same temperature and it would glow dimly red (plus lots of invisible IR light.)
Ever heard the term “limelight?” That’s what lantern mantels are. Before electric lighting, gas lights were used, and lime (calcium oxide) was heated to give bright white lighting. It was used in theaters and even used for searchlights. Camp lanterns do the same: it’s “limelight” but with thorium rather than calcium (but “thorlight” doesn’t have the same historical connotations.)
Limelight chem class demos
I wonder why camping lanterns use such delicate mantels, rather than using a solid hunk of lime? Maybe a mantel heats up instantly, whereas it would take many seconds before a chunk of lime was hot enough to give out blazing light. And maybe the problem is that lime deteriorates faster.
PS Today lantern mantels are Yittrium oxide rather than Thorium oxide. The thorium is weakly radioactive: not good to inhale particles of radioactive ash.