Ideal for entertaining kids, or summoning the dark knight to the scene of a crime.
IKEAhackers highlights (pun not intended) this very simple hack, which takes a Skimra lamp and adds an engraved plastic circle to create the Batlight effect.
IKEA Australia doesn't appear to sell the Skimra, but there's no real reason you couldn't modify another existing light, such as the $9.99 Kajuta to the same effect, although it would pay to keep the bat symbol well away from the bulb.
Calling for BATMAN! [IKEAhackers]