Risilights: the nearest thing yet to transparent stone you can actually buy?
RisiLights are used to illuminate walkways, steps and terraces. RisiLights are available to match both the Pisa2 and StackStone retaining wall systems (may also be used with RomanPisa or RomanStack Ashlar retaining wall systems).They are manufactured to the highest quality standards and are shipped complete with instructions. The only additional items needed are the light bulb and the appropriate underground electrical cable. RisiLights are ready to be installed using a conventional 110V power supply. If you prefer, a 12V power supply may be used, but the light socket provided will need to be replaced with an appropriate low voltage light socket.
A timer or photoelectric control unit may be used with RisiLights, but should be installed at the power source. This allows all of the units in that circuit to be centrally controlled. Multiple units of RisiLights may be connected in a parallel circuit with a second external wire continuing to the next light through the second opening in the rear of the unit.
Still, it's pretty! Check out this pic from Risistone's catalog:
[RisiLights via Oh Gizmo]

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I wonder how tuff they'll be. At any rate it looks like it may just be the final replacement to glass bricks *shudder*
http://farm3.static.flickr.com/2272/2076317885_8c6108323d.jpg
When I was in Istanbul on vacation I saw something similar to this. There were some streets that were paved with little stones, and on the edges of the streets, there were "fake" stones that lit up at night in different colours.
http://www.flickr.com/photos/nourmalaeb/3058918042/
http://www.flickr.com/photos/nourmalaeb/3058919576/
http://www.flickr.com/photos/nourmalaeb/3058920596/
I think that glass bricks are cool.
There are things for which I will pay $140 a brick. This is not one of them.
Check out the manufacturer website :
http://www.LumaStone.com
Very cool products :-)