An illuminating idea is spreading a new kind of light on the city streets, making them, city officials hope, safer in the process.

Walk Center City at night and you may notice some street lights lack their typical dull yellow glow. An example is this picture provided by the city streets department.

On a number of blocks downtown, high-pressure sodium lights, which produce the yellow hue, have been replaced with bright white Light Emitting Diodes through a $2.1 million pilot program that, city officials say, may eventually lead to new street lighting city wide. The newly lit area is bracketed by Race, 12th, 17th and Walnut streets.

On Race and Arch streets, from Broad to 12th streets, 119 14-foot lamp posts evocative of a small town lighting replaced cobra-headed, 30-foot light poles. The lamp posts match similar pedestrian-friendly street lights in the city, but are also equipped with LEDs. Some pre-existing pedestrian lights south of Market and west of Broad also received the LED fixtures.

"We wanted to lighten up Center City," said David Perri, the city streets commissioner, "make it feel safer."

The city installed the LEDs were installed from July to September. Brightening all the city's 100,000 street lights with LEDs would cost about $66 million, Perri said.

The advantages of LED illumination are three fold. They have a functional life of 10 years, compared to the 5 years high-pressure sodium lights last. They're 50 percent more energy efficient. And, perhaps most importantly, they create light more friendly to the human eye. Colors are easier to see and the lights improve peripheral vision and reaction time for drivers.

Cobra head lights were built mainly to illuminate the streets, Perri said. Sidewalks were an afterthought. Think about walking late at night, slipping in and out of a street light's amber halo and deep shadows. The LED lights are not bulbs, but are made of cells which can be aimed differently, allowing them to light street and sidewalk. A number of other cities, including New York City, are moving to the LED fixtures.

The new lighting for the city came up during the oft mentioned (in this blog, anyway) Vision Zero conference earlier this month. I've quoted this stat repeatedly here, but that's because it strikes me as important.  We've got some of the most dangerous streets in comparison to other big American cities, averaging 11,000 automobile crashes from 2009 to 2013 and 90 to 100 deaths annually. Those are worse rates than New York City, Chicago and San Francisco.

LED lighting definitely makes the streetscape brighter and is more energy efficient. Whether it is effective in making streets safer for pedestrians and bikers remains to be seen. Police release crash stats annually, so right now no data is available to evaluate the pilot program. But the city will be looking closely at those numbers, Perri said, to see if there's a measurable impact on safety for motorists, pedestrians and cyclists.