The twin beams of light are displayed to honor the victims and those who worked so hard to get New York City through its greatest trial.
There was a special viewing of the light display in the memorial plaza until midnight.
The memorial's lights were briefly turned off twice Friday night, to clear birds from the area as a precaution.
New York City Audubon members and volunteers were at the scene taking shifts counting the birds flying around in the beams. Every time 1,000 birds or more are circling, or an exhausted bird falls to the ground, they turn off the lights for 20 minutes.
88 7,000-watt xenon bulbs project the shape of the twin towers four miles into the sky.
It's the strongest shaft of light ever projected from earth.
The lights will fade away at dawn Saturday.