I found a wonderful instructable here:https://www.instructables.com/id/Create-Homemade-Fluorescent-Black-LightUV-Display/ and used his ideas to fill my test tubes with fluorescent highlighter ink. Less really is more when it comes to fluorescence, a fairly weak solution worked best for the level of light I wanted.
I found an old chemistry set in a charity shop a year ago and used one of the two test tube stands and three test tubes. I mounted the joule thief on a block of wood I cut from a jenga game - stuck him on the chemistry stand with epoxy and used thin rope I had left over to cover the wires. I was kindly advised to wire the (UV) LEDs in parallel and that is what I have done.
I like the fact the light is economical, running on batteries which are dead to most intents and purposes, plus I've always wanted to enter a competition here and now I have!