This is a "POCMARK" -- a term coined by Zoz to describe a solar cell, capacitor and LED connected in parallel. I whipped this together in less than 5 minutes with a 24x33 solar cell, 5.5V .047F Gold Cap and a flashing LED (FLED). Mr. Pock takes a few minutes to begin blinking under my 40W desk lamp, but it continues to blink for about 10 minutes after the lamp is turned off. A nice beacon to add to your BEAM park! I imagine that if the FLED were replaced by an IR LED, this could act as a homing beacon for other robots as well...