The last time I experimented with UV Black Lights was during the making of my Fluo Ditty Bag, this bag had lots of fluorescent Yellow UV reactive cord used to make a very happy bright bag; as you can see below.
Above and below: Under Natural light and also under UV Black Light.
After making this bag I did not get around to playing with UV again until now; when a friend asked me to make some pineapple knots for him. one of these was to be bright, and as you can see below, under UV light it fills that requirement quite handsomely.
This is a 40p x 36b, 6 pass, Type 5 Pineapple Knot.
Below: under normal lights.
And from the top under UV again.
Playing with UV Black Light is fun but only in very small doses; and with protective glasses, even then I still got a headache taking the pictures.