Edit: Rusty answer won and it's better
The main difference is that "lumbre" is made by will, and "fuego" can be started by will or not.
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Please, don't hesitate to correct my English.
'Time is a sort of river of passing events, and strong is its current; no sooner is a thing brought to sight than it is swept by and another takes its place, and this too will be swept away.' M.A.