http://vector.tutsplus.com/tutorials/illustration/how-to-create-a-vector-light-bulb-icon-with-inkscape/

Today we’ll be learning how to create a vector light bulb icon with the free, open source vector program Inkscape. We’ll be following a Tango style of design for this project. Read on to learn more about the Tango Desktop Project and to learn how to create this icon.