Well, not quite everything, there are little flickers of living light - bioluminescence.
Compared to most biological processes, bioluminescence is incredibly easy to evolve, requiring only an enzyme and substrate, the worryingly named luciferase and luciferin. Luciferase, at least in insects, appears to have evolved from a bog standard type of enzyme, the fatty acyl-CoA synthetases, whilst luciferin evolved from the substrates of these enzymes. Presumably because of the simplicity of this system it appears to have evolved on a multitude of separate occasions, in invertebrates, vertebrates, and fungi - about 90% of deep sea organisms, for instance, are believed to show some form of bioluminescence.
For those who would like a more in depth description there is an excellent review at....
The brightest luminescent insect in the world, and a native of the Mata Atlantica, is Pyrophorus noctilucus. It is not a firefly, but a type of click beetle, and unlike the fireflies the light is on all the time, though it can vary the intensity. It has two luminescent areas just behind the head, and one normally hidden under it's wings, As you can see from the video, it gives the distinct impression of having headlights.
The intensity of the light is about 1/40th of that of a candle, and the peak wavelength is 540nm, conveniently the maximum sensitivity of the human eye. It has been claimed that the light is strong enough to read by (though you have to hold it VERY close to the page!).
Interestingly the related species in Jamaica, P. plagiophthalamus, has different varieties from yellow/green to orange, controlled by a single gene mutation. So not only can they find each other at night, they are colour coded!