You take a cold cathode light (basically car neon) and set your shutter speed on your camera for a really long time, I usually do around 30 seconds, and walk around/wave the light at night time. Since the light is so much brighter than everything it shows up as a continuous streak of color.
I had a whole shit ton of led cables on different timers while dancing at bisco. Saw some cool pictures. Never painted with light but got some pictures of a weird acid jellyfish of colors with the exposure.
the light that the light puts out is stronger than the light that bounces off you body. but if you stay in one place to long the camera will pick up parts of you.