> The bulb is a prototype "fluorescent" light he invented consisting of a partially evacuated glass bulb with a single metal electrode. Nearby, probably behind the curtain, there is one of his Tesla coil high voltage oscillators which produces a radio frequency electric field. The electric field ionizes the gas in the bulb, causing it to glow similar to a neon light. This photo is a 2 second time exposure taken by the light of the bulb
https://commons.wikimedia.org/wiki/File:Nikola_Tesla_holding...
> The bulb is a prototype "fluorescent" light he invented consisting of a partially evacuated glass bulb with a single metal electrode. Nearby, probably behind the curtain, there is one of his Tesla coil high voltage oscillators which produces a radio frequency electric field. The electric field ionizes the gas in the bulb, causing it to glow similar to a neon light. This photo is a 2 second time exposure taken by the light of the bulb