Bob Koslosky <102365.2062@compuserve.com> asks:
> Can you elaborate on this seeming anamoly?

It's an efficient way of lighting an underground city several
miles across; you can open or close it to allow the big vessels in for
construction purposes, and so on. If you build something that big, you
need some way of getting stuff IN there, then lighting it without
consuming vast amounts of energy.

jms