To paint abstract forms with light, you have to start with a very dark room -- not absolutely black, but close. The LED headlamps I use are the type popular with mechanics and campers, and can be found in most hardware and camping supply stores, as well as online.
The Gerber Triode ($20, street, www.gerbertools.com) is inexpensive and has perfect LED spacing and a long battery life. I also recommend a digital camera, because this technique relies heavily on trial and error to get the exposures and the shaping of the light trails right.
The instant feedback I get via the LCD makes it more fun than chore-like.
I shoot at night, because it's much easier to get the room dark then, and I wear dark clothing to minimize the possibility of showing up in the picture. I put my Canon EOS Digital Rebel with a 28-80mm f/3.5-5.6 Tamron lens on a tripod, setting the ISO to 200 and the drive mode to Self-Timer.
My starting exposure is usually 5 sec at f/22. The small aperture prevents overexposure, which can lead to the background room showing up in the photo, and it keeps the LED lines sharp and flare-free.
The next step is framing and focusing. I decide where I'll be during the exposure, and set the focus for that location using my Rebel's manual focus mode.
Next, I set the zoom, so I'll be able to fill most of the frame with light during the relatively short exposure. If I set the zoom too wide, the light streaks will be small, and I may not be able to make it across the frame within the few seconds that the shutter is open.
I start with a focal length between 28mm and 40mm, and a subject distance of about 8 feet. Then, I practice with a few "fake" exposures to get the timing down.
Holding the lamp in my hand, I pace my movements so I get from frame edge to frame edge across the duration of the exposure. If I dally in one part of the frame, the light will "clot" there, risking overexposure.
To make the first test exposure, I turn out the lights, turn on the LED, start the self-timer, and position myself in front of the camera. Just before the shutter opens, I begin to move around, trying to make it as even and smooth as possible. (Anyone seeing me might think it was T'ai Chi.)
As soon as the shutter closes, I run over and look at the results. I check exposure and the light shapes. Almost every image I make inspires me to try another. I continue to fine-tune the movements and shutter speed until I get abstractions that I like.
For a fun variation, you can put colored gels over the LEDs. If your camera allows it, try multiple exposures. Experiment with writing words. Or tie the LED lamp to a string and swing it for smooth arcs or whole circles. Just don't let go of the string!
To see more of Josh McCullock's photography, visit his website, web.mac.com/joshmccullock.