Just as autumnal darkness has begun to linger at the beginning of the day and arrive earlier at the end, Pittsburgh is countering with an extravaganza of light.

Last weekend Downtown shimmered beneath a colorful cacophony of fireworks in celebration of the city's 250th anniversary. The Pittsburgh Cultural Trust's International Festival of Firsts sparks off this weekend with the U.S. debut of an art installation centered around a 40,000-watt carbon arc lamp.

And Friday evening the Agnes Katz Plaza will become a magical place as the energized sound of Pittsburgh jazz legend Etta Cox and her band, along with CAPA student guests, sets the mood for the debut of the Pittsburgh 250 Festival of Lights.

The free concert begins at 6 p.m. and will continue until 9 p.m. At 8:30 p.m., with the flip of a switch, a flood of saturated color and vibrant patterns will pour onto the wall of the Century Building behind the Louise Bourgeois fountain.

It's the work of French lighting producer Lucette de Rugy, executive director of Artlumiere. Many readers will remember the painting-like lightworks that transformed facades at Katz Plaza, the Omni William Penn Hotel, the Highmark Building and Duquesne Light last summer. Rugy, and specifically designer Corentine Buron, have returned to illuminate Katz and the William Penn Friday through Nov. 20.

Construction around the other two sites precludes lighting them this year, but more than compensatory will be the extension of the festival into Oakland, where two sides of the 535-foot-tall Cathedral of Learning and the Stephen Foster Memorial on the University of Pittsburgh campus will be lighted beginning next Wednesday.

The festival's first movement piece has been designed for Katz Plaza, a three-minute repeating work. The William Penn projection relates more directly to the city's anniversary, both by association with the hotel's namesake and inspiration from "perhaps our state flower" (the mountain laurel), according to festival director Marguerite Jarrett Marks, who doesn't want to give too much away before opening nights.

Rugy invited a German design team, Casa Magica (Friedrich Foerster and Sabine Weissinger), to create the Oakland lightworks, which reflect the symbolism of the Cathedral of Learning and pay homage to it. They've made two projections, the first of which will run during the first half of the festival, and then be replaced by the second.

While the two Downtown sites will be welcomed in by jazz singer Cox, the lighting of the Oakland buildings will follow a zany, free performance by Pittsburgh originals Squonk Opera, a band/theater/performance art/visual art melange that's entertained audiences from here to New York City and beyond.

Squonk will present the Pittsburgh debut of "Astro-Rama" at 8 p.m. Wednesday in Schenley Plaza, and the Cathedral turn-on will follow.

Free performances of "Astro-Rama," which the Squonk Web site describes as "our response to the increased alien activity in the Mid-Atlantic region," will be at 8 p.m. Oct. 17 and 18 at Schenley Plaza.

The four buildings will remain lit from 6 p.m. until midnight daily, and other events will be held both Downtown and in Oakland. Among them will be a 7 to 9 p.m. Oct. 31 Halloween Family Fun Night with the Children's Museum, presented in partnership with the Pittsburgh Parks Conservancy, featuring activities and trick-or-treating in Schenley Plaza.

Plans for Oct. 23, 30 and Nov. 1 programs will be announced later.

Music will continue to fill Katz Plaza from 6 to 9 p.m. on October Fridays. On the 17th, a special floor will be rolled out on the plaza so visitors may dance to the Latin stylings of Americas Latin Orchestra (formerly Azucar). On Oct. 24, the Neon Swing X-perience re-creates an era of zoot suits and romance, and Oct. 31, the Downtown Halloween party (costumes encouraged) will feature Jessica Lee & Friends Rhythm Jazz & Blues.

While nothing is formally scheduled for November, festival spokesperson Lissa Rosenthal predicts a variety of "buskers and street performers will organically appear."

All events will be held weather permitting. There are no rain dates or alternate indoor venues, Rosenthal says, "but the lights will be on rain or shine -- or snow."

New to the light festival this year are several activities that broaden its scope into the community.

"Our Community Gallery" is a 30-by-50-foot virtual gallery that will project works by students in a variety of disciplines onto the side of the David L. Lawrence Convention Center. The six-minute projection will include painting, sculpture, poetry, dance and more by local K-through-12 students and their mentors.

Also at the convention center, Jenny Holzer's public art light work "For Pittsburgh" will remain on in the evenings, as will the Water Feature. Inside, The Children's Museum's "Stories of Children" installation will be on view in the east lobby during normal center hours.

Throughout Downtown, Oakland and suburban locations (such as the Sri Venkateswara Temple in Penn Hills), 18 places of worship will light their buildings, accentuating their aesthetic and historic components and inviting considerations of the meaning light holds in religious belief.

The festival will also direct visitors to existing city features that relate to light, such as artist Doug Aitken's "Migration," a component of the 2008 Carnegie International "Life on Mars," projected upon the exterior of Carnegie Museum of Art, and the Carnegie Science Center's "E-Motion," which will have special lighting during the festival.

Some restaurants will join in with "A Little Light Fare" during Restaurant Week, which returns Nov. 3 to 9 and features prix fixe three-course lunches and dinners.

The Pittsburgh light festival is not only the largest of its kind in the United States but, in fact, the only one, Rosenthal says. The festival inspiration is an ongoing event in Lyon, France, which began in the 19th century, when residents lit candles in their windows in thanks to the Virgin Mary for answering their prayers to spare them from the plague epidemic.

Tours of the lights are being offered by Molly's Trolleys (412-281-2085) and Just Ducky Tours (412-402-3825). Information about other events will be posted at pittsburghcelebrates.org beginning Friday.

"At the end of the day," Marks muses, "it doesn't matter if someone comes Downtown to attend an event and discovers the lights, or comes to see the lights and discovers a restaurant."

"We're bringing families and communities together," adds Rosenthal, "to look at art, at our history and at the future."

For more on artist Lucette de Rugy: Pittsburgh Celebrates Glass: French artist will paint four Downtown buildings with light and French artist is eager to turn Pittsburgh into 'City of Lights'.