When Wendell brought this home from Costco awhile back and told me about it, I barely paid attention. I humored him and said, "Oh, cool!"
But let me tell you, when you suddenly don't have electricity and are engulfed in darkness, IT IS TOTALLY COOL! It is a lightbulb with a built-in rechargeable battery.
You screw the bulb into wherever you normally have a lightbulb. While it's in normal use, it is charging itself.
And when you lose power, the bulb recognizes this and STAYS LIT automatically. The box says it'll stay lit for up to 10 hours. We were out for 30+ hours so it didn't last the whole time, but it was so handy in the beginning. The 6-pack was under $20.
Here's the bulb at work in our bathroom.
And this is our light in the bedroom. SO, SO COOL, WENDELL!