The "13" for the 2013 that will light up when the ball drops in Times Square on New Year's Eve arrived in Times Square today. Andy Dallos headed over there to greet it as they took it off the truck. The NY1 coverage mentions:
The number includes 32,000 high-power LEDs. They use only 9 watts each, compared to the 40 watts that the previous halogen bulbs used.
Not mentioned in the report is where they keep the "20." I never tried to look, but I guess they could just leave it up there.