Photographers like Eric Curry and Harold Ross have created beautiful portfolios full of artful images of outdoor subjects, photographed after dark and illuminated with gelled strobes and/or flashlights during the course of minutes or even hours. This is, obviously, a beautiful application of the technique. But, it can also be done—in fact, it's a bit easier to accomplish—in a little dark room with a smaller tabletop subject. That's where I suggest you start learning to light paint. Here's how.
First, choose a subject and position it far from the background as you would with any "normally lit" subject. This way you can control the exposures independently, without the background affecting the subject, and vice versa. For this example, I chose an old electric fan.
Next, get your tools ready and have them staged nearby. This step is important, because in a moment you're going to be working totally in the dark—the last thing you want to do is stumble around in the pitch black darkness. I have a roll-around cart that works as the perfect shooting table, and I position it near my camera (which is set on a tripod, after composing the scene normally with the lights on) for easy access to my lighting equipment.
For the next step I find it's easiest to use a cable release that allows you to keep your hands off the camera. It's not mandatory, but be forewarned that every little bump and nudge of the camera will come back to haunt you, should you try to composite multiple exposures together in the end. (More on that in a minute.) I use a locking cable release made for my camera, and with the exposure set to Bulb, I can lock the camera open until I release it again manually. Alternately, pre-timed long exposures of 30 seconds or more, depending on the kind of camera you're using, will accomplish much the same thing—as long as you're able to complete the painting in the allotted time.
As for camera settings, I start with the lowest available ISO and a middle aperture—say, ISO 100 and f/8. This way I'm choosing a sharp aperture and low-noise ISO that lends itself to long exposures. I can always adjust both as needed—whether to increase the light sensitivity, shorten the exposure duration, or to modify the depth of field. The benefit of a long exposure is that it's easier to time the exact duration of your lighting; small changes make less of an impact.
When you're ready to begin, turn off the lights: It's time to get painting. I purchased a compact, yet powerful flashlight made by the fine folks at Maglite. I bought it purposefully, wanting to maximize the intensity of the light in order to keep the exposure times to a minimum. This is a good idea in theory, but in practice I may have overdone it. My light purports a maximum output of 130 lumens. It might be a few too many, because when I've got it going full bore it blows out everything other than the shortest exposures. That means that I've got to stop down more or just paint for a brief moment or two. Painting for only a moment makes it hard to make precise, subtle changes in technique--and these are what light painting is all about.
The saving grace of my ultra-powerful flashlight is that I can use light modifiers on without completely squelching its output. The main modifier I use is a length of plastic conduit—the kind found in the electrical aisle of your favorite big box hardware store for only a couple of bucks. The 90-degree angled piece I use not only reduces the intensity of the light output, but it focuses it slightly, while at the same time taking the edge off of the bare bulb. This means I can position myself and my flashlight where they will paint effectively on the subject, without creating lens flares and without my hand or my body blocking the shot.
That's one of the major challenges with light painting—getting your light in the right position and keeping yourself and your tools out of the shot. Angled PVC pieces can be helpful with this, as can affixing little black flags to the side of the flashlight that faces your lens. Because remember, any appearance of the light source itself will register on the sensor, and in your picture. (This can actually be beneficial, if you're interested in creating streaks of light as I did to represent the moving air in my fan shot. For that, I simply aimed the flash toward the camera and moved it in a back-and-forth motion to create the streaks of light.)
I've got a faux fiber-optic attachment for my flashlight. It's something I picked up years ago from an outfitter, and I couldn't tell you the specific intended application in the wild, but this little five-inch-long tube delivers just the perfect pinpoint light wherever you may need it. A similar effect can be achieved by rolling aluminum foil (especially the black kind) into a tiny little snoot for a flashlight. The benefit of this is that you can shape the opening, however you see fit to really customize how it falls on the subject.
Another great modifier for serious light painting is the colored gel. These translucent sheets can be held or taped over the light source to change the color from neutral to red or blue or whatever color gel you have on hand. Want to warm up part of the scene? A warm orange gel might be just the ticket. Best of all only a few square inches—much like you'd put over a hot-shoe flash—are enough to get the job done.
As for painting technique, it's a fairly simple process of trial and error. I like to start by painting on a key area of the scene for an allotted amount of time and checking the LCD to see whether I need more exposure or less. Then I make adjustments and go from there. I do this for every different part of the shot I'd like to paint: subject elements, background elements and any other areas in the scene that I'm going to address with individual attention from my flashlight. The whole time I'm painting, I'm also counting: one Mississippi, two Mississippi… and paying attention to approximately how far from the subject I'm holding my light. It's these two factors—time and distance—that ultimately impact the finished exposure. Remember, the camera exposure remains unchanged from exposure to exposure.
When you get one part of the scene looking just right, you simply make a mental note of how long you painted that spot (how many Mississippis you counted) and where your light was positioned. On a particularly complex setup, you may even want to write these things down to keep it simple.
For my fan shot, I started with an exposure that lit the base for a few seconds, and then each blade of the fan for 10 seconds. I then did an exposure on the background with a streaking unmodified flashlight for just two seconds, and then a good five seconds of the flashlight visible in the frame behind the fan to create those windy streaks. I also did a three-second exposure with the flashlight focused on the emblem in the fan's center. Lastly, in most cases you may want some sort of overall fill—either from a flashlight through diffusion or even a brief flash of the room lights—to build up an overall "base" exposure and add a general bit of fill light. In this particular shot I didn't incorporate an overall exposure like this, but it can be a pretty powerful way to add more detail and a hint of realism to this otherwise otherworldly effect.
Once I've got a handful of separate exposures of various scene elements I could simply take the best of each element and composite them together to create an overall light-painted composite shot. There are some challenges that come from blending such exposures, but ultimately it's a pretty useful technique. In this case, though, I went on to take the information I gleaned from each of the individual elemental exposures to create one single all in-camera shot in which I lit each element independently. I simply worked off of those notes—how long to paint each blade, how long for the background, etcetera—and in the end created a pretty workable image. Better yet, I can still composite in any individual elements, or even tiny little pieces, from one of the test shots that may have worked better.
Ultimately, light painting is a wonderfully interesting and improvisational technique that's a holdover from another era. It's one of the few things that's still best accomplished, if not downright inimitable, in camera. Sure, you can always composite multiple exposures, or come up with your own digital painting technique, but it's a lot less interesting—not to mention less fun—than tromping around in the dark with a flashlight in your hand. It's one of those blessed situations when good ol' fashioned physics wins out, because nothing compares to the look of actual light falling on an actual subject.