LOS ANGELES — On bright days, the rooftop of the Anaheim Hilton Hotel is so blindingly white that it looks like a mirror positioned directly at the sun. That dazzling glare might just be the greenest thing to happen to the top of a building since solar panels.

The white coating deflects nearly 85 percent of the heat that hits it, reducing the surface temperature by as much as 50 degrees. That means less energy is needed to cool the hotel's interior, cutting air-conditioning costs and carbon emissions.

This is no ordinary coat of paint. Designed by an 82-year-old former military scientist from the Inland Empire, the tinted topcoat is filled with tiny hollow glass balls that deflect heat, layered over a waterproof undercoat made of recycled rubber.

The Hilton spent more than $150,000 on the project, which was completed in March. That's $300,000 less than the cost of conventional repair to the old leaky roof, said Jerome Annaloro, director of property operations at the hotel.

If the reflective material cuts utility costs this summer the way management anticipates it will, Annaloro said, he will recommend white roofs for the entire Hilton chain.

"I was skeptical at first ... but the product spoke for itself," he said. "It's a win-win."

Americans spend about $40 billion a year to cool buildings, according to U.S. government figures. "Cool roofs" are touted as a simple, inexpensive way of lowering surface temperatures on the tops of structures by as much as 100 degrees, cutting operating costs and slowing climate change.

Secretary of Energy Steven Chu, a Nobel Prize winner in physics, recently called for all roofs to be painted white to promote saving energy. Some scientists suggest that covering dark tar roofs with light-colored coatings could help mitigate the "urban heat island" effect. Development has raised temperatures markedly in many cities, leading to more energy use and smog and greater numbers of deaths during heat waves, experts said.

But it will take more than the Hilton to make a dent.

"To change an entire city and save energy all the way around, you need to get to a critical mass," said Scot Horst, senior vice president of the U.S. Green Building Council's Leadership in Energy and Environmental Design rating system. "One or two buildings doesn't make that big of a difference."

Mass implementation of cool roofs in the 100 largest cities would offset 44 billion tons of carbon dioxide emissions, or the equivalent of taking 600 million cars off the road for 18 years, according to researchers at Lawrence Berkeley National Laboratory. Some cities, including Chicago, already have ordinances that require light-colored roofs.

Skeptics say white roofs aren't always the eco-friendly panacea they're made out to be. The reflective component is most effective in sun-saturated regions like the Southwest. And it could lead to higher heating bills in the winter because the sun's warmth can't permeate the roof.

Still, the niche is booming. The Energy Department and U.S. Green Building Council are pushing cool roofs to consumers and developers. Entrepreneurs are developing a host of new products using metal, ceramic tile, reflective paints and coatings and even rooftop gardens to beat the heat. Among them is Ronald R. Savin of Rancho Mirage, a serial inventor and holder of nearly 20 patents, who developed the paint atop the Anaheim Hilton.

Hyperseal paints are free of harmful volatile organic compounds (VOCs), and are relatively cheap to produce, but the company's Palm Desert factory can make only 5 million gallons a year. Most large projects, such as bridges, require several hundred-million gallons, Savin said. So he's looking to license his formula to other companies.

He'll have plenty of competition. Big players including Sherwin-Williams Co. and Benjamin Moore & Co. are also debuting eco-friendly paints.

Still, Savin's product is winning a following. In addition to the Hilton and the roofs of dozens of homes, the rubberized undercoat now covers a large swath of pavement outside a Palm Desert Wal-Mart.