Any times I know of where a Japanese guy goes by Aki, it's part of a longer name. Here are some of the other meanings of Aki, depending on which kanji character you use: glitter/glisten bright (different kanji than the one for light) chapter of a book pleasant/cheerful
Aki is the first name of the heroine in the film "Final Fantasy: The Sprits Within." Since the name means "born in autumn," it suits her perfectly, since the character has an autumn birthday.
Angela Aki, a famous singer and songwriter bears the last name "Aki". Her father, Kiyoshi Aki is the founder and owner of AEON Institute of Language Education, which is widely used in Japanese schools today.