“A ‘light painting’ digital photograph is created by the movement of a light or lights, using a slow camera shutter speed to create an image.”
Most photographers work with a one second to ten second exposure, but any exposure that shows the movement of light in front of the camera will work.
The use of a regular flashlight with an LED bulb will work just fine and gives out a clear white light. You can also use a mini-mag to diffuse light or portable neon lights for a variety of colors. A dark environment is usually essential for this type of photography, and keeping the ISO as low as possible will reduce the amount of noise in the photograph.
Initial Starting Exposure: Try starting with an ISO of 50, a shutter speed of 4 seconds and an f/stop of f/8. If the picture is underexposed increase the ISO and/or lower the f/number and/or increase the shutter speed. If the picture is overexposed, shorten the shutter speed and/or increase the f/number of the lens opening (aperture).
Helpful information: http://www.rickdoble.net/paintingwithlight/light_painting_index.html