A question on lightning

[Atellus]

Hello. I wonder if someone could answer a question on a particular aspect of lightning?

 

Why do positive streamers appear purple in colour?

 

Thank you

[YT2095]

Ionisation energy of the gasses they pass through, if you look at the Spectra for Air in specific for Nitrogen, you`ll see it has Many bands in the Purple wavelength.

I don`t have the Spectral data for O2 and Argon to hand, but they may also be worth looking up, look around the 400 nm band.

[Atellus]

Thanks!