I've never used blacklight for Christmas but I use it extensively for Halloween. What kind of black light source are you going to use? From my experience, standard incandescent black light bulbs do not produce much UV light. I get the best results using black light fluorescent tubes. The attached photo is my graveyard. Styrofoam tombstones with fluorescent paint from a craft store to outline the words. I misted fluorescent spray paint on some of them so they would glow. Blue works best but you have to be careful with spray paint because the solvent will eat the styrofoam. I used that property to texture some of the tombstones then I painted them with gray latex house paint and that protected it from the spray paint I misted on afterwards. I've been using them for over 10 years without touching up the paint. It is really effective, but the light source is a shop light with two T12 4' bulbs so it is very strong. I also have a few 18" black light fluorescent fixtures. You can buy the special ones that are sold as black light units. Or you can buy the cheap 18" fixtures and replace the bulbs with black light bulbs. You save about 50% by going this way. This year I built a water resistant UV light source using the same work light case used for the Aether and a blacklight CFL. The CFL produces a lot more visible light in comparison to the standard T12 tubes. Probably not a big issue for Christmas decorations but comes into play for Halloween decorations where you want it to be dark as possible.
