Work with time. Try making something that is only visible in a long-exposure photograph. Drawing with a laser pointer, flashlight, or a sparkler in the dark are a few options; you can even create an image by moving the camera itself. If you don't have a camera that can do the job, see if a friend can help.
I used the 'fireworks' mode of my trusty little Olympus Tough camera for this one, and moved it around to capture the light of a single tealight candle. The letters were made one at a time. Super fun!