Mercury arc rectifier

[ppppenguin]

"seem to be just the regular florescent tubes without a phosphor" with a special glass to let through the UV, not quite quartz but better than soda glass for transmission (of UV).

As I understand it, there are two types of fluorescents that are designed to let out UV. They all generate plenty, it's just how much gets out. It's possible the gas filling is tweaked on some types to maximise or minimise UVB and UVC.

One type, often called blacklight blue, gives out mainly UVA with a filter to minimise visible light. Often used in clubs etc for visual effect. The other are the germicidal tubes, giving lots of UVC. Presumably these tubes are quartz. Used for sterilisation and EPROM erasure.