My Google-Fu is weak on this one. I've had this idea since I made a fiber-optic flashlight in the Air Force for the guys that had to crawl into the aircraft fuel tanks. Basically we found some real thick (about 7/8") fiber cable and slipped most of it inside some Black rubber tubing. By exposing about a foot of one end and making an adapter that fit onto a high powered spot light, we could have a well lit work area inside the fuel cells with no worry of any fire caused by the lighting. Don't know if it got approved for use. This was a project that was being done on the side, not officially sanctioned, by a group of maintainers. The gov't approved method still had risks that this one didn't. I know lighting like this is being done commercially, that us where the idea came from when we made the light back then, several years ago. Basically the concept is to find thick fiber-optic cable, I'm thinking at least 3/8 inch diameter. It doesn't have to be high-grade like what is used for data transmission, only be able to transmit light. The basic idea is similar to a solar water heating panel. You would build the panel just like a solar water heating collector. Except that instead of piping you would put the exposed fiber that has been very finely scratched to best capture the light. Then you simply run the fiber through you house exposing the fiber and scratching the outer surface where- ever you wanted lighting. You could build fixtures as needed to help filter, enhance, or block the sunlight as needed. Be a great sealed system that could light those bunkers without using up electricity. The fiberoptic cable could be routed and sealed just like electrical wire. Just don't put any tight bends in it or you lose some of the light gained. My problem is finding the fiber optic cable. I wasn't the one that found it when we built the light although I was the one that designed that system. If anyone knows what I'm talking about and can point me in the right direction and provided the fiber isn't outrageously expensive. I will be more than happy to update everyone on my progress with building the system.