Blacklight is UV-A, and doesn't have much use other that detection of things like blood and making posters glow (and non-destructive testing to look at things like weld penetration and cracks in metal.) While it's pretty harmless in short exposures, long-term can cause cancers. It's just slightly above violet in the spectrum, so you see a little bit of dull purple glow. There's not enough visible light to be of any use as an illumination device.
Chances are what you are experiencing is people misunderstanding the LED lights that are replacing Mercury Vapor and HIgh-Pressure Sodium lamps. White LEDs work by exposing a phosphor to a blue LED die, giving you white light. Some lamps are cold white, and have a bluish-purple glow similar to what you'd see from a blacklight.
Non destructive testing uses UV
Yes, you are right. I've never dealt much with that end of equipment, it escaped me.
On a side note I've seen a few LED street lamps and lighting already give out or flicker.
IMO sodium is still superior. Much easier on the eyes and the bulbs can actually last for a pretty long time.
Yes. LEDs have infant mortality problems. I've seen mercury vapor lamps on for so long they're green and you can hear the plates in the starter transformer chattering.
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