Light painting is a tecnique to control lighting in photography. Also flash photography is a simple light painting, because you choose where flash is pointing, how much powerful it is, which colour its light is. But this tecnique could be very complicate too, as you can see with a simple Flickr search
My contribution at this nice modern art has been done in different ways, with a neon light
, with a led stripe
, and even with car's headlights
Now I explain you how to build a neon paintbrush.