Graffiti Light

Check out what these kids are doing with an extended exposure and a bag full of lights.

Their flickr photos even includes brief instructions:

this is a small collection of flashlights, biking-lights and flashing LED lights they all work with batteries so that you are mobile you also get nice results with fireworks & torches .

there are 3 different type of lights we use:

xenon: makes a warm golden light.
LED: makes a thin precise line.
cold cathode: thick line.

but the best results you get by experimenting, use filters and things witch reflect light.

HOW TO DO IT.

this are the basics:
to get the best results you need a tripod. the exposure should be around 10-30 sec. or longer if needed. stay in front of the camera and do your writing.
to not overexpose set the camera to about iso100, and close your aperture as much as possible. if there is still too much light you might have to use a nd-filter.
it is always nice to integrate the surrounding into your picture.

View more here.