Another cheap little toy I recently acquired is a keychain containing a multicolor LED that rapidly flashes between red, blue and green. It looks white (almost) to the naked eye when it’s stationary, but when it’s moving quickly enough, persistence of vision allows you to see the different colors. My webcam frame rate is timed such that it picks this up as well.
It’s been a reasonable distraction for when I’m put on hold by tech support or customer “service.”
yeah, I totally have one of those too, next to my desk!
An LED that has a “dim” setting often achieves that dim setting by flashing rapidly. So the persistence of vision in that case will stretch the motion into a set of dots. The closer spaced dots indicate something that was moving more slowly. You can do some neat motion analysis with this tool and a digital camera — check out http://www.flickr.com/photos/89476186@N00/sets/72157594539823950/