UV light or black neon (when turn off it is black/deep blue color neon)?
UV light is dangerous. Can irritate your skin and cause permanent blindness. Mostly used to kill bacteria. In aquarium, it is used to kill bacteria and algae too inside UV water filter. But it is not visible or exposed to human or fish.
Black light is neon that produce more UV light than normal, but still in safety range. You can stare at it if you like. It will bring out color of fish if put on aquarium.
Which one?
Regards,
Arto.