We did a search when we picked the name, and found https://github.com/xopxe/Lumen. I emailed Jorge to ask if he was ok with us using the name for a Lisp-to-Lua project and he sent a delightful reply that began "It's impossible to avoid conflicts with such a cool name", and pointed out that there were other projects called lumen that he discovered when he published on Github. Who knows how far back the lumens go.
By now finding great names that aren't in use yet (let alone not in use in a similar context) is almost impossible. Fast fwd 100 years from now & we'll have way more artifacts with names. I think we'll be fine.
https://lumen.laravel.com/