Fun little interactive project by Olafur Eliasson from a few years ago called Sunlight Graffiti.  Beautiful imagery…

Description from the site:

The Sunlight Graffiti sphere is by artist Olafur Eliasson, conceived as part of his larger Little Sun project. An interactive Sunlight Graffiti installation is set up at Tate Modern, London, on level 2 as part of the museum’s Poetry and Dream exhibition. Visitors are invited to do a work of art here by dancing, jumping, and writing out loud with a Little Sun in their hand. Their Sunlight Graffiti are captured and uploaded to this site and shown as part of the sphere.