The spindly man walked quickly with one hand resting in the small of his back, a smoldering Dominican cigar wedged between his bony fingers. Down a hall, up a flight of stairs, he came to a fortresslike door and swiped his identity card over a security sensor.

"In here," he said, stepping inside the room. Before him, like a futuristic Stonehenge, stood a semicircle of black monoliths, all electronic equipment.

Nearly every bit and byte of the contraption was this man's brainchild. This man being David Niles, the 61-year-old technological and creative director who invented the eye-popping wall of moving images in the Comcast Center.

Normally, he checks in on this control room - the cerebral cortex of "The Comcast Experience" - via cameras connected to his studio in New York. But this week he was in Philadelphia to produce a new feature for the wall. Outside on the Comcast plaza, he had just left the crews who were setting up the stage and equipment. A cast of Broadway dancers was warming up for its dance number. And Niles was already imagining how he would integrate the film shot later that night into the Holiday Spectacular show - a series of ultra-high-resolution videos that would be processed through the ultrasophisticated machines in this room and then viewed on the ne plus ultra screen in the lobby.

All year, the public is free to watch the videos in the lobby. Women in billowy skirts seem to be descending from the ceiling in circus lyras, office workers seem to dance on the ledges above the elevator banks, and the Earth viewed from space seems to orbit into the room.

For the winter holidays, though, Comcast has introduced a new tradition, giving the classic Wanamakers Christmas light show a run for its money. The video will be featured on the Comcast lobby wall from Thanksgiving until Jan. 2. And although it took Niles two days to film and many more to edit, the segment shot on the plaza this week will take up 1 minute, 49 seconds of the 15-minute show.

Niles is a decorated knight in the field of high-definition television. (He's worked on projects at Radio City Music Hall, Madison Square Garden, and the Shanghai Expo, and collaborated with Mick Jagger, Aerosmith, and Crosby, Stills & Nash. And he produced the Broadway show Dreamtime.)

Late Tuesday afternoon, a large staff and crew, musicians, producers, hairstylists, makeup artists, a choreographer, and a dozen Broadway dancers converged on the communications giant's headquarters. They spent two days, working from sunset until 1 a.m.

"I need a sheen!" Niles commanded. "Can I please have someone get a garden hose?"

Two workers who had been emptying bottled water onto the stage stopped what they were doing. Niles shook his head disapprovingly, and his long gray hair knotted in a bun flopped against the collar of his pin-striped sports jacket. He ran his fingers along the wet surface. "We're never going to have puddles like that," he said.

The stage had been constructed in front of two rows of fountains. When filming began, they'd be shooting 12 feet into the air, misting the rubberized floor. Concerned that the dancers might slip, Niles asked for a test run.

John Dietrich, the choreographer, began the count: "Five, six, fivesixseveneight." The dancers leaped and kicked, pirouetted, and hydroplaned.

Niles and his crew had the engineers lower the front row of fountains to six feet. Then, for the next two hours, they all waited. Niles ordered a pizza, polished off a Perrier, and lit up his second cigar.

Meanwhile, in one office on the skyscraper's upper floors, costume designers hustled to finish, sewing red trim along the hems of black-and-white polka-dot swing dresses. In another office, makeup artists dabbed humidity-defying minerals on the dancers' upturned faces.

At 9:58, spotlights started sweeping the sky. "Snow machine up!" Niles called, and a flurry of soap and alcohol flakes shot into the air.

"Clear the set!" he shouted. "Fountains. Fountains. Fountains. Fountains. Fountains. Who's got fountains?"

Plumes of water burst from the ground.

The dancers, who had been stretching in the lobby, were summoned. Testing the traction, one woman consulted with Dietrich, who ripped off a few pieces of tape and stuck them to the soles of her shoes.

"I'm slipping," she explained to Niles, who smiled sympathetically.

"It's one of those moments," he said. "Do it with a smile."

The women, in halter dresses, had been given red cardigans to wear up until the last moment. By the time the show appears on the screen, they will look as if they're running around sleeveless in the dead of winter. The illusion won't be that far off.

By 11 p.m., the temperature was approaching 50 degrees and the wind had picked up.

"Sweaters off!" Niles said. "Quickly! Run! Run!"

"Jingle Bell Rock" began to play. The couples poised, waiting for their cue. "Here we go!"

And they did.