"Please sit down and greet the light," Jon Landau instructed as visitors arrived at the new Chestnut Hill Friends Meeting House the other day just before sunset. By "sit down," Landau, a meeting member, actually meant "lie down." And by "greet the light," he meant, be prepared for Philadelphia's most entrancing new art installation.

In preparation for a public showing of Skyspace, a wordless narrative of light and color by internationally renowned artist James Turrell, yoga mats were unfurled on the floor of the bare white sanctuary. People reclined on the handmade wooden benches. Children cozied into the parentheses of their parents' arms. Everyone gazed heavenward, waiting in silence for the show to begin.

And then, without anyone realizing it, it did.

A retractable cover glided off the meetinghouse roof, revealing a patch of late-afternoon sky through a square aperture in the vaulted ceiling. The square turned a deep cerulean blue, and the china white of the ceiling softened to eggshell.

Ever so slowly, the square deepened to violet as the ceiling segued to yellow. Soon the square was turning green and the background was taking on a rosy glow. Then green was contrasted against mustard. Turquoise against yellow. And so it went - for 50 minutes. As time passed, birdsong became audible. A jet plane painted a black diagonal stripe across the blue square. Stars came out, first as points of light, then as a densely speckled field, the way they look in places far north of Philadelphia.

Finally, as though a lightbulb had abruptly burned out, the square went black. It was the exact moment of sunset.

It may not sound like much of anything, but Turrell's Skyspace is likely to turn this modest Quaker meetinghouse on Mermaid Lane into a prime Philadelphia art attraction, on the order of Claes Oldenburg's Clothespin or Robert Indiana's LOVE sculpture.

Turrell, a white-bearded wizard, is already an international art star. He was recognized over the summer with a career retrospective at New York's Guggenheim Museum that was made up entirely of fleeting works of light.

Turrell is also something of a computer-age Johnny Appleseed: He has made it his mission to build Skyspaces around the world. The one in Chestnut Hill is No. 84, and it is the first year-round version on the East Coast. Skyspace will be open to the public on Tuesdays and Thursdays, at sunrise and sunset.

A little meetinghouse in Chestnut Hill might sound like an unlikely place for one of his coveted and costly art pieces. The Society of Friends eschews any decoration in its meetinghouses, which are famously plain. But because Turrell, who is himself a Quaker, creates artwork that has almost no physical properties and is intensely spiritual, it managed to pass muster.

The Philadelphia Skyspace is Turrell's second in a Quaker meetinghouse. He installed the first in 2000 at the Live Oaks Friends Meeting in Houston, and it immediately became a sensation. When he learned the Chestnut Hill Friends were also trying to raise money for a new meetinghouse - the city's first since 1931 - he offered to give them a Skyspace if they could pull it off.

The Friends opened their new home in the fall, a decade after they acquired the two-acre site off Germantown Avenue. The project, designed by Bryn Mawr's James Bradberry Architects, struggled for many years, and last Christmas it was hit with a cruel act of vandalism that police attributed to a union dispute. But the Friends carried on.

The new home, next door to the former meetinghouse, is a modern rendition of the traditional form, partly covered in local Wissahickon schist. Significantly larger than the old meetinghouse, it will allow the Friends to expand their programs, hold special events, and offer shelter to homeless families. But it will no doubt be best known for the Skyspace.

As promised, Turrell showed up this month to put the finishing touches on the computer-controlled light show.

Words like art and sculpture don't begin to describe Skyspace. The long immersion in shifting light has a way of forcing you to concentrate on the properties of specific colors in a way that rarely happens in life. "His work clearly demonstrates how people see light differently," said Gail Harrity, president of the Philadelphia Museum of Art and a Turrell fan who sprawled on the floor of the Chestnut Hill meeting to watch a recent showing of Skyspace.

Focusing the viewer's attention on the sky is an obvious metaphor for the divine. It's probably no accident that Turrell starts off his computer-controlled sequence with blue and white - the colors of heaven and earth. It all fits in with Quaker belief, which uses light as a metaphor for the divine.

Even though the artwork disappears when it's turned off, it is still possible to think of Skyspace as a descendant of the great religious art that decorates the ceilings of Renaissance churches to medieval mosques. Instead of biblical figures or intricate patterns, Turrell uses light to guide the eye toward the celestial realm. His square aperture is effectively a portal to the divine - one that seems in perfect sync with our screen-obsessed age.