If you've ever taken a photo at night as a car drove by, or as you were sitting in a car, looking outside, you've probably seen this effect. You've probably captured these "light trails" that can sometimes be pretty impressive. These almost ghostly images are the result of long exposures. Well, take it to the next level, and you get "Light Graffiti." Light Graffiti is a technique using long exposures, up to 30 seconds at times, to capture trails of light.  (Don't get it? follow me...)

Here's an example. This was captured using a tripod, standing in the middle of the Burnside bridge in Portland (is he crazy? yes! He is!). The buildings are stationary, so the camera captures their lights as discrete points. But since the cars are moving, the light becomes blurred and appears as a light trail.

In this example (also in Portland), the light trails are warped as cars are turning onto an on-ramp outside of Hotel Fifty. Where are the cars? Since the cars are moving fast, they don't appear in the photo because the camera doesn't have enough time to "capture" them. OK so you've seen all this before right? Here's the reverse.

In this example, the camera is moving. So, instead of getting steady trails of light, we get a nice little seizure effect.  This was a 2 second exposure sitting in my friends car. As we blasted down the street I tried to hold the camera as still as possible - this is why the dashboard of the car is still somewhat visible.

Here is the same effect, exercising a little more restraint. On our way home (after a few drinks) from an Italian restaurant, I noticed this dark intersection that had several focal light sources (traffic lights, street lamps, buildings etc.)  The exposure wasn't quite as long so I don't get as much of a crazy swirl of lights. But, with the car in motion, bouncing up and down, it created a "Z" pattern of lights. Camera Zorro!

O.K. So we clearly understand what long exposures can do to create some interesting light effects. However, in both examples above, we couldn't really control the light source. Well, what if we could take a bunch of colored lights (flashlights, glowsticks) and move them around in front of a camera?

This is Light Graffiti - the art of painting with light. Don't worry, it's totally legal! (as long as you don't litter your flashlights and batteries when you're done!)The most common Light Graffiti images I have seen include drawing smiley faces, or printing messages in light.  Well, being overly ambitious, I wanted to take it to another level and incorporate a subject into the photo as well. But first, I had to experiment a little go figure out how this works.

 Experiment 1 
 First, I setup my tripod in a dark room, and set from a long exposure (anywhere from 10-15 seconds).  Aiming a flashlight at my face I would sit down for 5 seconds, turn it off, and re-locate to another position, and turn it on again, for 5 seconds. In this example, the subject (me) is lit, but you don't see the light source (where's the light trails?). Well, since the flashlight wasn't pointed at the camera, it won't "see it". Cool huh? This is one method of achieving multiple exposures / images or the "multiple personalities" photo. 

 Experiment 2 
For this shot, I started by shining the light on my face in a dark corner (top right), then aimed the flashlight at the camera (bottom left), then ran towards the camera with the light pointed at my shirt. You can even see the pocket on my shirt towards the bottom right. The trick is, you have to do all your painting and motions in reverse (like looking into a mirror). You also have to think spatially where your trails are, so they don't overlap!

This is hard! I GIVE UP!... Okay I'll keep going.

 Experiment 3 
Long exposure at 13 sec of my guitar with light trails generated from a large-bulbed flashlight. By continuously moving around my guitar, I was not captured in the image. The long exposure allowed the guitar to be exposed well, but also exposed the background, which I didn't want. One way around this, is to do this in a bigger space, but since I didn't have a room large enough to do this, I came up with an alternative solution.

Experiment 4
I shortened the exposure time to about 10 sec, so ambient light (background) is minimized. But, in order to keep the guitar exposed, I had to use flash. So the sequence was as follows:

1. The Camera's shutter is triggered, and my flash (set to front curtain sync) goes off. This captures the guitar only.
 2. As the shutter remains open, I ran the flashlight around the guitar to capture the light trails.

This is a somewhat more pleasant outcome, but I don't like the glare and reflection off the guitar. You can see my tripod and camera set up in it. Plus, you can still see some of the background being exposed by the power of the flash (despite bouncing it behind me)

 
 Final Shot 
Ok, so I eliminated flash, and kept the exposure to about 10 seconds. This meant the background was blacked out (except a bit of the blinds to the left) which is great, but the guitar wouldn't show up all that well. So for this final sequence, I did this:

1. Paint the guitar first - I aimed my flashlight for about 3-4 seconds on the strings, the neck, so these areas would be exposed and appear to be "glowing" from the light streaks.
2. I ran the flashlight around the guitar in those same areas that I had previously painted.
3. Apply a cyan gradient to half the photo for kicks.

PHEW! That was exhausting, but I think I have a pretty good handle on Light Graffiti.