Latinlacking

Lucem fero.

Just as an aside, these words are the roots of the name "Lucifer".

Understood. While doing my own research I found "Lucifer" meaning "bringer of light", but figured that the person who asked me was unlikely to want that for a personal motto. I also found "Adfero Lumen", but wasn't certain that was appropriate. There seem to be rather a lot of Latin words meaning both "bring" and "light".

Yes, "adfero" also means "I bring". The prefix "ad" adds the sense of "bring to".
"Lumen" also means "light" and is often used to mean "a light" or the source of
light. The correct syntax using those words would be "Luminem adfero".