Probably not what you think... a UV LED Flashlight! I was in Harbor Freight and saw their cheap UV light, for like 6 bucks! I picked it up and shined it on my watch... holy crap!! Of course I had to have it!
I was sitting here tonight and thought, "Hey, I have a drawer full of watches (one of many!) and it's night time... duh!"
Ran down the hall (in the dark), went into the back room and opened the drawer. I turned on the torch and couldn't believe it! The whole drawer lit up! I showed a before and after shot, just for comparison. There are about 50 watches in the drawer, anywhere from the 1920's to the present and probably 75% of them have some sort of lume (those '20-30's watches really popped!). The pix do not do it justice as the human eye has to see them in person to appreciate all of the lume after your vision has adjusted to the light. Even my new Galaxy S10 didn't do very well - probably me not knowing how to take a longer exposure. Anyway...
Everybody, run out and pick up a UV light and give it a try... it's a trip y'all!! Be sure and post up your pictures. I have no idea if an expensive UV Torch works any better or not. Let me know.
One more thing... when I was done I looked around the room with the UV and couldn't believe all the "spots" on the carpets, walls, peeked in the bedrooms, bathroom, etc. That's a whole nother dimension of, "freakin out"!!