The technology is described in this Wikipedia article. The bottle is acting as a light pipe. It doesn't create any light itself, it just transfers sunlight outside the building into the building.
Here in the UK light pipes aren't much used, probably because electric light is cheap and natural light tends to be rather variable. And of course light pipes are absolutely no use when the Sun is down. In parts of the world where sunlight is more reliable and cost is more of an issue I can see how useful the idea would be.
Re your question about using a longer tube: I suspect you're thinking of something along the lines of a fluorescent tube, but this isn't how the light pipe works. You could probably adapt the pipe to make it leak so light came out of the side as well as then end, but the light would be rather dim as it's only transferring the light that hits the end of the tube that sticks out of the roof.