Scatter spooky blacklight accents throughout the room to enable a Dr. Jekyll and Mr. Hyde transformation when you flip off the regular lights and turn on the blacklight. For example, use paint that is invisible in regular light but glows under blacklight to paint an enormous spiderweb in one corner of the room. Add a few ghostly silhouettes -- perhaps hovering hauntingly beside a couch or over a bed. Spooky blacklight accents would be particularly appropriate for a Halloween party or a room in a "haunted house."
Sprinkle tiny fairy silhouettes trailing showers of specks (fairy dust, of course) to give your blacklight room a magical touch. Buy or make a fairy silhouette stencil, and apply paint that glows under blacklight over the stencil. The stencils could be applied randomly throughout the room, concentrated on one wall or in orderly rows along the bottom of the walls for a glowing fairy border. A fairy blacklight room would be especially enjoyable for a young child or a magic-minded adult.
Fill the blacklight room with stars arranged in a spiral configuration to suggest the majestic swirl of a galaxy. Paint the stars with paint that glows under blacklight but is invisible in ordinary light so that when the blacklight is switched on, people in the room are suddenly plunged into the heart of the cosmos. The galaxy could be restricted to a single wall or encompass the entire room -- that is, all walls plus the floor and ceiling.
Paint a mural on one wall of the room using only shades of paint that glow under blacklight. The mural could be anything from a written message ("Smile, it's a beautiful day!") to a pattern of polka dots to an intricate landscape scene. Place a single blacklight near the base of the wall to illuminate the mural in a dramatic fashion.