First referenced in the Arrow episode "The Man Under the Hood," Dr. Light in this instance will be the female version of the legacy hero/villain.
The "classic" Doctor Light is a villain named Arthur Light who troubled The Flash, the Teen Titans and other DC heroes. Eventually a female version was introduced named Kimiyo Hoshi, who was a hero and served on the Justice League International.
In the New 52, the pair were revealed to be married -- although Kimiyo hasn't yet appeared as Dr. Light in the new continuity.
Prior to the relaunch, Arthur Light had become one of DC's most controversial characters, loathed by fans for his role as a rapist in the best-selling miniseries Identity Crisis.