How do you say light princess in Japanese?

Answer 1

Akari-hime or Hikari-hime.

That surely is a right translation, so no offense, but if you mean the novel by George MacDonald, I think "重さのない姫 (omosa no nai hime)" or sth. alike would be more appropriate, though it's difficult to say because it's kind of a pun and could also be meant in the sense of taking sth. lightly as the princess in the novel does.