Hmm, I wish I could. Keep in mind I'm by no means an architectural expert yet. I'm only in my second quarter.

I checked the glossary in my huge art history text and laylight wasn't mentioned, but based on the context of the Smithsonian article and the results of a Google search, it sounds as though it's something like a stained glass window in a ceiling.

I have the magazine, so if I remember, I'll ask my art history prof on Tuesday.