Prometheus associated with light because Prometheus was a Titan who is credited with bringing enlightenment to humans. He stole fire from the gods, and gave it to mankind, bringing the power of warmth and light to the dark and miserable earth. By doing this, he angered the gods, who wanted to keep the power of fire and enlightenment for themselves. So Zeus, king of Olympian gods, punished Prometheus by chaining him to a rock in the Caucasus mountains. Every day, his liver was devoured by a giant eagle, only to regenerate overnight. Generations later, the great hero Heracles came along and released the old Titan from his torture.
So, due to stolen light and spreading it to Human Light is associated with Prometheus.