blacklight (n.): an external window in a large space habitat, looking out into space (see: the black). The word was deliberately coined in opposition to skylight, since due to the operation of spin gravity, the majority of blacklights are in the floor.

It is considered both polite and practical to throw a rug over the blacklights when flatlanders come to call.

– A Star Traveler’s Dictionary

(Well, no-one’s going to call an UV light a blacklight when they can see UV natively, are they?)