Something strange is happening to downtown San Francisco. In an alley off Market Street, larger-than-life flowers sprout on the sides of a building. The top of the Ferry Building is twisting like it was thrown into a blender, and near the Embarcadero BART station, a building's wall has become a book, pages flapping in the wind. As they encounter these transformed facades, passersby stop to stare.

The hypnotic displays are part of Let's Glow SF, an annual free light show by the Downtown SF Partnership, the community benefit district behind the Drag Me Downtown pop-up drag performances and free block parties. At 7 p.m. on Friday, Mayor London Breed flicked on the lights at what its organizers call America's largest "holiday projection event," turning shadowy buildings into canvases for psychedelic lighted artwork. Powerful projectors beam custom animations onto several buildings in and near the Financial District, and crowds gather to watch.

And these aren't just any video projections. They're artworks tailored for specific downtown buildings, designed to play with their brickwork, molding and silhouettes. On Front Street, colorful bubbles climb the columns of the Pacific Coast Stock Exchange. Another projection on the Exchange makes its facade look like it's crumbling. From Embarcadero Plaza, you can see gears turn in the spire of the Ferry Building, before the scene transforms into a candlelit tower.

These are works that require a time commitment, for both the artists and the audience. Ryan Uzilevsky, CEO and creative director of New York's Light Harvest Studio, said he spent some 700 hours working on "Enchanted Solstice," for the front of the Ferry Building. Walking around the area, you'll notice passersby standing at plazas, their necks craned upward. For the most part, they don't speak. They just look up, tracking the laser snowflakes with their eyes as music pulses from the speakers behind them. On Market Street, one delivery driver got off his bike to film the display at 1 Bush St.

Let's Glow SF's organizers said the program brought around 67,000 people to the Financial District last year and pumped $8 million into San Francisco's downtown. Robbie Silver, the president and CEO of Downtown SF Partnership, told SFGATE he expects this year's projection show will draw between 80,000 and 100,000 people downtown, depending on the weather.

For one San Francisco building, the dazzling display is permanent. An art project called East Cut Electric transformed the homely PG&E substation at 425 Folsom St. into a concrete canvas for projections. From sunset to 10 p.m. every evening, colors swirl up and down the 171-foot-tall building.

The rest of the artworks are just temporary installations, meant to celebrate the holidays for a short time, like "A Winter Tale," which animates the story of a frost giant who turns a village into a winter wonderland. Darina Maulana of the Indonesia-based studio The Fox, The Folks, which created the piece, said it was "such an honor" to have the studio's seasonally themed work projected onto a building.

Let's Glow SF runs through Dec. 15 from 5:30 p.m. to 10 p.m. On Dec. 13, Downtown SF Partnership plans to pump up the festivities with a block party on Front Street, California's first "entertainment zone," where restaurants and bars can sell to-go drinks for outdoor enjoyment during certain hours. The glow-themed party is expected to shut down the street with a dance party on an LED dance floor, a black-light mural and live music.