13-08-2024, 11:14 PM
Tanning salons using florescent tubes cause skin cancer. The cheapest UV tubes for resist exposure (screen printing in late 1970s) seem to be just the regular florescent tubes without a phosphor, but the one in my old insectacutor seems filtered. Our current death-to-flying-bugs seems to use violet LEDs in tubes. That makes the yellow phosphor on the filament stick style LED lamps glow.
Also some washing powders and laser / copier paper have "brighteners" and fresh whites or copier paper can be very bright white with UV or violet light*.
The RGB model as used by displays and cameras works mostly, but doesn't quite match the human response, so visible violet LEDs (beyond blue but not actually UV) can be looking much bluer via camera and screen.
However many sensors have poor IR and UV rejection so white balance on tungsten or bright sunlight can be off. I have UV filters for all my DSLR lenses and they make a difference.
[* It's of course nonsense that a rainbow has seven colours. Newton deliberately picked 7]
Actual magenta / purple is light without the green, not a spectrum colour at all. But visible far violet spectrum causes some reaction to the red sensing in our eyes, so for some people the monochromatic violet just past "blue" looks purple like magenta, i.e. white light with green blocked or mixed red and green light. So a really good camera feeding a regular RGB display shouldn't look blue with near UV "violet" light. It should look closer to violet by using a blueish magenta.
Also some washing powders and laser / copier paper have "brighteners" and fresh whites or copier paper can be very bright white with UV or violet light*.
The RGB model as used by displays and cameras works mostly, but doesn't quite match the human response, so visible violet LEDs (beyond blue but not actually UV) can be looking much bluer via camera and screen.
However many sensors have poor IR and UV rejection so white balance on tungsten or bright sunlight can be off. I have UV filters for all my DSLR lenses and they make a difference.
[* It's of course nonsense that a rainbow has seven colours. Newton deliberately picked 7]
Actual magenta / purple is light without the green, not a spectrum colour at all. But visible far violet spectrum causes some reaction to the red sensing in our eyes, so for some people the monochromatic violet just past "blue" looks purple like magenta, i.e. white light with green blocked or mixed red and green light. So a really good camera feeding a regular RGB display shouldn't look blue with near UV "violet" light. It should look closer to violet by using a blueish magenta.
