Hikari can also be a boy's name. I know because I personally know a man who has this name (and I'm absolutely sure he's called "Hikari" and not "Hikaru" like most boys/men would be called).
Though "Hikari" happens to be my Japanese name (chose it myself because I like the concept of being a light to others), it's not so common in my generation. I think most girls named Hikari are under 20. The kanji for this name can also be pronounced "Hikaru" and is much more common as a name and is used for boys OR girls.