Why we bring the light outside
More than 2,000 years ago, the Maccabees, a small band of Jews, drove the Syrian-Greek army out of Jerusalem and took back the Holy Temple. They found a single jar of pure olive oil, enough to light the Temple’s menorah for one day. It burned for eight.
So Chanukah lasts eight nights, and each night we light one more flame. The menorah goes where people passing by can see it, to share the miracle with everyone. A parade of cars with menorahs on their roofs takes that light down every street in the neighborhood.
These links open Chabad.org.