Similar to Picasso’s famous light paintings, Air Pencil is a phone app that lets you make extraordinary 3D paintings with light. Via FastCoDesign:

Triple exposure of artist Pablo Picasso drawing w. light at his home in Vallauris. (Photo by Gjon Mili/The LIFE Picture Collection/Getty Images)
http://www.fastcodesign.com/embed/da54b24313166?rel=1&src=embed&veggiemode=1
sparklers!