There are also solid state LED bar Graphs with 8 and 10 LEDs molded in solid plastic, which you can use to create LED chase patterns or to test code. These will work with the BAR resistor as well.

Further Investigation

The History of the Interface in Interactive Art Söke Dinkla http://home.snafu.de/mediainmotion/1994/dinkla.html

Article on Contestational robots. http://www.appliedautonomy.com/objectors.html

Robot Builders Sourcebook by Mcomb McGrall Hill

References:

[1] Waldman, Jonathan Faster than the blink of an eye
(http://elixir.bu.edu/apr3003/hotspot/photonics.htm)
[2] Cambell, Jim Artists web site: http://www.creativetime.org/artonplaza/images/ campbell.jp
[3] Dan Paluska, Jessica Banks, jackbackrack
[4] http://www.appliedautonomy.com/documents.html
[5] Holzer, Jenny, image complements of ImageMD