Rulings on the Sunlight spell

During Session 113 of my DF campaign, questions came up about the Sunlight spell.

It's a spell I think is underused, and perhaps because of that it hasn't really come up before in our game.

Can I cast it in mid-air?

In other words, can I cast it above something to illuminate down?

I ruled no.

Area spells are cast on "the ground or floor" per Spells, p. 12. This neatly solves the issue of "cast it on the air in front of me at -0 and illuminate things very far below me." That would essentially mean it's easy and cheap to light up distant, deep places. Instead of PCs exploring with trepidation down crevasses and fissures or into strange sinkholes, they'll just cast Sunlight and have a look down. Not for this game, no.

Why doesn't the sunlight spill out into the surrounding area?

It does, sort of. The light is still light, and illuminates an area outside of its radius to a lesser effect per Exploits p. 19. But it doesn't spill out; it acts as if it's a light projected from above.

But it extends up?

Yes. Someone argued this makes no sense. Well, it's internally logical, in that it creates a light source on the sky or ceiling above that projects light down. It's weird in some circumstances, but it's magic and not that unusual for that.