The Spectrum of Lightning

Forked Lightning Spectra

Denis Joye captured these lightning spectra during a thunderstorm over Paris. They reveal the extreme conditions inside a lightning stroke.

He used a 540 line/mm diffraction grating in front of the camera lens. A slit is usually needed to get good line spectra. Here the very narrow lightning strokes make a slit quite unnecessary.

We see sharp spectrum emission lines superimposed on weaker continuum light.