.. Or I suppose that should be fire by light. Of all the methods used to light fire this is probably the easiest and least energy expending method out there, you would use more calories striking a match than getting an ember this way.
It's been raining a lot here but I took advantage of the sunny spells inbetween to try out my Hudson Bay Tobacco tin, ember medium was char cloth
Virtually the instant the focal point of the lens was reached the char cloth caught fire, it was nearly instantaneous!
I'm sure we've all done this as kids but I simply forgot just how effective this method of fire lighting was!
There's no excuse for not carrying a lens even if it's a Fresnel lens, it does the job just as well
again, it's virtually instantaneous!
and provided you have direct sunlight, it's a practically unlimited resource for making fire.