None bulbs are kind of fascinating— in part due to their ability to act as relaxation oscillators [1]. I found an old electronics hobbyist magazine going into details [2] (Man, I love the linked site, BTW, so many awesome old electronic projects to pore over.)

[1] https://en.wikipedia.org/wiki/Relaxation_oscillator

[2] (Starts page 21—as printed in the corners of the pages) https://www.worldradiohistory.com/Archive-Elementary-Electro...