I love geeky products, especially when they are somewhat green.

From Thinkgeek.com:

Captured inside the Sun Jar are a highly efficient solar cell, a rechargeable battery and low energy LED lamps. When the jar is placed in direct sunlight the solar cell creates an electrical current that charges the battery over a few hours. This energy is then used at night to power the three LED lamps inside the jar.

The light is diffused by the frosted jar and give the appearance of sunlight emitting from the (warm colored LED lights are used to give a more natural and warm light).  You may have noticed that there is no switch on the Sun Jar - in fact there are no visible controls at all - but there is a clever light sensor inside that automatically activates the LEDs when it gets dark or the lights are turned out! (There is an override switch inside the lid to turn off the light at night and conserve battery life.)

More products should be like that: self sustaining and energy efficient.