The fibers can transmit light up to 50 feet, and because they take up only a small portion of the block, they do not affect the structural integrity of the building material.
Filled with optical fibers that run from one end of a poured piece of concrete to the other, these prefabricated blocks and panels effectively transmit light from one side to the other. Colors and light remain remarkably consistent from end to end, but with a natural variation from the pouring process that actually softens the effects considerably.
Link - via darkroastedblend
From the Upcoming ueue, submitted by Minnesotastan.