Longwave 365nm UV Lights: Blacklight Tubes vs. LEDs
365nm UV light is often called "blacklight". Before the advent of longwave UV LEDs, blacklight fluorescent tubes, (the kinds used in hippie days to light up psychedelic posters) were the standard longwave UV light for our hobby. They were not very powerful but they did light a large area.
The "black" glass, really a deep violet, acted as a filter. It allowed UV, usually 365nm, to pass through but blocked most of the bright whitish light the fluorescent bulb produced. We say "most" because a lot of violet/purple light still escaped, illuminating our rocks with a violet tint, not the best. Additionally, since these blacklights were not very bright (not much UV) and spread over 18", only the most reactive fluorescent minerals "glowed" under them.
Enter 365nm UV LEDs
Around 2014, powerful UV LEDs became economical enough to replace fluorescent tubes as the standard for our hobby. MinerShop released a distributed LED system that used multiple LEDs to light large display cabinets (it has since been discontinued once lighting manufacturers got on board with new products such as Engenious Designs distributed system, the LNKR).
Convoy released the S2 UV flashlight which became a game changer for portable UV flashlights. It didn't come with a filter so we provided instructions to install this absolutely required filter. LEDs still produce a lot of white light which must be filtered out.
So what's the best longwave UV flashlight?
Very hard to determine today given how many different types are offered. We did a limited summary but we need to do a serious evaluation of the most popular UV flashlights on the market, on the to-do list. Beware of outlandish power claims, many scams out there. And ALWAYS get a filtered UV flashlight.
Bottom line - fluorescent tube blacklights are a thing of the past. Filtered 365nm LEDs have completely replaced them. Don’t waste your money on tubes.
(Note: not the case with shortwave and midwave UV flashlights. Tubes are still the best performers, but 255nm LEDs are quickly gaining ground. Shortwave UV flashlights are all the rage now - I use them exclusively. )