James Turrell provides the stage. Your retinas, and that hard-wired brain of yours, put on the show.

Part painter, part sculptor and part magician, Turrell uses light as another artist might use acrylic or clay. He paints and sculpts with it, creating illusions that take advantage of the mind's perceptual predilections. He has distilled art into pure light aimed at our neural pathways.

"James Turrell: Into the Light," the 59-year-old artist's first major exhibition east of the Mississippi in decades, opened last month at Pittsburgh's Mattress Factory. The show provides a good selection of the artist's light works, most falling into a handful of types: ones that include partitions, ones that look like wedges, ones that overwhelm your field of vision and ones that employ simple projection. Each elicits its own strong reaction -- Turrell can disorient, surprise, enlighten or dupe. No matter what shape his pieces take, though, their aims are the same: to see what seeing looks like.

Turrell has zeroed in on light's presence, what the artist calls "the thingness of light." To him, light is something we can feel with our eyes, something to be molded into shapes that trip reactions in our brains.

Turrell's brilliant "Pleiades" provides a tutorial on the ways of seeing: After you feel your way into a near pitch-black room and sit there for 15 minutes, the show gets going. Under-stimulated retinas, it turns out, strike up their own tunes. I saw a purple haze waft across my field of vision. You might see something quite different -- white spots or shooting stars, perhaps. Whatever you see, it's what your retinas produce spontaneously.

Any museum hosting a Turrell show knows these pieces are demanding. Almost every one requires its own room. All depend on recessed lamps -- fluorescent, neon or incandescent -- that wash colored light over walls, ease it from behind partitions or project it directly. Sometimes natural light augments the electric glow. Most every piece is calibrated to the lowest light levels so that our pupils open wide and drink the color in. That's how Turrell transforms a room into an experience.

Turrell has spent years learning the eye's tricks. His works subject us to much of what he's learned: He studied perceptual psychology in college. A professional pilot, he's logged countless cockpit hours acquainting himself with the curve of the Earth, the many hues of blue and the disorientation inside a cloud deck. As a kid, he was fascinated by light's power to both illuminate and obscure. The stars, he knew, were always there, but we can't see them when the sun is out. It was an epiphany that turned light's reputation for illumination on its head. Now his art trades on light's chameleon-like properties, and our eyes' adaptation to it.

Remember, back when you were studying science in grade school, and your textbook asked you to stare at Figure 1, a red box sandwiched in its margins? You looked and looked and looked some more, and when you looked away, the world was green. Stand inside Turrell's "Big Red," a room lit entirely in crimson, and that early lesson in retinal compensation will come flooding back.

Other pieces encourage hallucination, not science lessons. "Catso, Red" projects a red light on a corner. The shape appears three-dimensional, like a floating red box obscuring the corner behind it. Reach out to touch it, though, and it's not there. Directing light in one direction or another, Turrell has discovered, has remarkable effect on how we see -- or don't see -- a box or a corner or a wall.

Some of Turrell's most beguiling pieces charge light with ambiguity. "Danae" is such a piece. When you walk into the gallery, it looks like a violet mural hangs on a wall twenty-some feet away. Step closer and the piece changes: The sheet of color seems to hover, a mirage, in the near-total darkness. Move closer still and a cutaway aperture in the wall is visible, with the light emanating from behind it. The temptation to reach a hand through is irresistible. But that first penetration of the light is frightening -- as if some electric shock might accompany the touch. (Washingtonians unable to get to Pittsburgh can experience something similar at the National Gallery of Art, which several months ago installed "New Light," a red version of a similar piece.)

Turrell is a skilled illusionist. He honed his skills, back in the late 1960s, over countless hours in his Ocean Park, Calif., studio spent playing light off its white walls and floor by selectively covering and uncovering windows. Chance ambient light -- reflections from passing cars or the sunset -- as well as artificial light danced across his walls.

Now he can make walls appear where none really exists. So successful are his illusions that some years ago a visitor trusted the solidity of a certain "wall" so much that she leaned against it, tipped over and broke her wrist.

At the Mattress Factory, you'd swear on Euclid's grave that an orange and yellow wall runs diagonally through Turrell's "Milk Run."

Sorry, folks. It's not really there. Just a ray of light in a room with corners that meet at right angles.

Just how wrong our initial perceptions can be is the great disorienting -- and liberating -- lesson of Turrell's work. Minds prefer to resolve unfamiliar situations fast, an instinctive response that saved many a caveman from wandering tigers. But such fast thinking can prevent us from seeing what's really there, and off we go leaning on something that doesn't exist -- psychologically as well as physically.

Like a fairy godfather, Turrell can also orchestrate wholesale transformation. His 20-foot cube of a building in the Mattress Factory's parking lot turns gray skies blue.

Turrell's constructed a number of these "Skyspaces," in various sizes, worldwide. All have large holes cut in the ceiling. Your job, once inside, is simply to look up at the sky.

The hole you'll look through in "Skyspace, Unseen Blue" is 11 feet square. Step inside, preferably at dawn or dusk when the sky is most dramatic, and take a seat on the reclining benches lining its walls. I went in at around 8 p.m., as dusk approached Pittsburgh's North Side. The yellowish illumination of incandescent lights recessed along the room's perimeter was faint; the sky above looked light blue. A half-hour later, as the sky darkened, the heavens seemed a deeper shade of blue. The room had warmed to a glow from the lights.

When I stepped outside and headed for my car, I looked up again, eager to catch another glimpse of a sky so perfectly cerulean. What I found was a sky turned flat and gray and thick with clouds. Those lights Turrell installed inside had transformed the sky. The phenomenon, to scientists, is called "simultaneous contrast." The result to my eyes was, briefly, miraculous.

The true measure of Turrell's ambition, though, sits in the Mattress Factory's basement. There, a 27-foot-long model of his Roden Crater project miniaturizes an idea of mammoth scale. For three decades and counting, Turrell has been burrowing into a mile-wide volcanic crater in Arizona's Painted Desert, destined to become his largest light work. The prime view will be from the inside of the bowl, which will frame the sky somewhat as the apertures in the Skyspaces do. The crater's round rim, though, will better mimic a pilot's-eye view of the Earth's curvature. No small goal, Turrell's aim is to bring the cosmos down to us. His crater -- he compares it to ancient sites in Ireland and Egypt -- is calibrated toward celestial movement. Its architecture is something like an observatory crossed with a bunker. Inside, he's carving chambers and tunnels reaching into and around the crater's bowl. Here and there, he'll cut holes to the sky. Four cutaway models on view here show the keyhole-shaped tunnels and sundry apertures through which light will pass. Working with astronomers, Turrell aligned his apertures with movements of the stars, sun and moon while accounting for the Earth's wobble and lunar slowdown. His project is built to last. Turrell calls it a "pre-made ruin . . . programmed to outlive our culture." Unlike his other projects, it requires no electricity. If civilization as we know it were to end, Roden Crater will still be up and running. Its accuracy, as far as lunar and solar alignment are concerned, will be at its height 2,000 years from now. If the power goes out then, so be it. With the aid of science and the artist's remarkable will and intellect, the seemingly preposterous goals of the crater project -- like so many of Turrell's schemes -- are now attainable.

James Turrell: Into the Light at the Mattress Factory, 500 Sampsonia Way, Pittsburgh, Tuesday-Friday 10 a.m.-5 p.m., Saturday 10 a.m.-7 p.m., Sunday 1-5 p.m., to April 30. Admission $6. For more information: 412-231-3169 or www.mattress.org.

Trading on light's chameleon-like properties, and our eyes' adaptation to it: James Turrell's "Catso, Red," left, and "Skyspace, Unseen Blue."Turrell's "Danae" seems to morph as the viewer's distance from it changes.