At the recent CALS meeting we had a night session to look at fluorescence. The lack of UV reaction from some flashlights demonstrated that some were better than others. 

The criteria turned out to be twofold: 365 nm and a visible light filter on the front of the light. Many UV lights are 395 nm, and these don't work as well. Also without the filter, the blue and violet light coming from the flashlight can drown out the reaction. By polling my friends I can now recommend 3 flashlights. But any others with 365 and the visible light filter should work too. Here are 3

I use UV Beast V3 mini. This did very well at night, and even was able to show Lepraria pacifica and the medulla of Parmotrema arnoldii fluourescing blue-white during the day.

Jason Hollinger likes the Alonefire brand

Damon Tighe uses Convoy C8

All are available on Amazon. 

Ken Kellman