Oggz rechargable LED mood lights
Oggz (as seen on Shiny Shiny) are squishy, rechargable silicone eggs with colour-shifting LEDs inside. They hold charge for a minimum of six hours but have been known to last ten to twelve. The light is completely self-contained - you can juggle with them, which is apparently quite impressive looking by night. £40 from The Gadget Store.
Being self-contained, you can use them in the bathtub (according to getoggz.com), or quite easily create custom lamps. They're 3.5" tall or 4" when on the charger. Left on the charger, obviously they remain lit permanently, so this might be a more practical option than the Happy Blackout if you're expecting power fluctuations.
[GT]
