In the early ’90s, I had a column in Mondo 2000 magazine (called “Street Tech,” BTW) covering DIY high-tech. I profiled a guy — I forget his name — who was doing “electronic graffiti” in NYC. He was building simple LED flasher circuits into little RadioCrap project boxes, and attaching them to lamp posts, street signs, the sides of buildings, etc. He would even set up timed events between a string of these boxes (e.g. a series of boxes on Stop signs would flash in sequence down the road). I thought it was tres street tech/cyberpunk for its time.
Over a decade later, and the idea lives again, this time, under the auspices of The Grafitti Research Lab. They’ve published instructions online for making “LED Throwies,” simple LEDs bundled with a battery and a rare earth magnet so the Throwie will stick to street signs, mail boxes, and any other “ferromagnetic” surface. These are nifty. I’m definitely going to make some.
On the Instructables project page, a reader has a great tip. If you use conductive epoxy or solder to attach the LEDs (instead of tape) you’ll get more power from the magnet, and if you use flashing LEDs, you’ll get MUCH longer battery life.