Unless my memory forsakes me, there was Coke Light many years ago and then Diet Coke. The website says that Diet Coke became Coke Light in April of 2007 (it is called "Non-calorie Coke" in Japanese, ノーカロリー コカ・コーラ). Then Coke Zero was introduced in June of 2007 and appears to be taking over.
A vitamin fortified version of Coke Light has just been introduced, so that might be where they are taking the brand.