365nm UV light is often called "blacklight". Before the advent of LW LEDs, blacklight fluorescent tubes, (the kinds used in hippie days to light up psychedelic posters) were the standard LW 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. I 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 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.
Around 2018 a few members of our Facebook group got together and designed the C8. This exceptionally bright light changed the hobby. New LW fluorescent minerals were discovered almost weekly. We published the design (open source) and dozens of companies copied it, in the USA, China, and worldwide. One even claimed he held a patent on it. It has become the standard in the hobby that others try to imitate.
Today there are dozens of C8 copies on the market, some very good, some very poorly designed. There are also many display lighting systems using LEDs. There are also many really cheap flashlights, LED light strips, and other knockoffs. Many don't have filters and are useless for our hobby. Lots of them are 395nm or 405nm, also useless for our hobby. They are really just violet light and cannot be filtered. All your rocks will look purple.
MinerShop recently released a turnkey 365nm LW lighting system, the GloBox.
With this complete turnkey system using bright LW LEDs inside a shadow box you can display your rocks in even brightly lit spaces.
What's the best LW flashlight?
Very hard to determine today given how many different types are offered. I did a limited summary but we need to do a serious evaluation of the most popular lights on the market, on the to-do list. Beware of outlandish power claims, many scams out there. And ALWAYS get a filtered light.
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 lights. Tubes are still the best performers, but 255nm LEDs are quickly gaining ground. SW flashlights are all the rage now - I use them exclusively. )