This is the 419th most frequent Italian word.
luca
"Luca" is a proper noun, typically a male given name in Italian.
Here, 'Luca' is used as a proper noun, a person's name, specifically the name of the speaker's best friend.
Luca è il mio migliore amico.
Luca is my best friend.
In this instance, 'Luca' still acts as a proper noun, referring to the author of the novel mentioned.
Ho comprato un romanzo scritto da Luca.
I bought a novel written by Luca.
Here, the word 'luca' does not apply; the correct Italian word for 'light' is 'luce.' This would require correction.