Santa Rosa has been working to slash its PG&E bill ever since the recession knocked its budget's lights out four years ago.

It started by darkening thousands of its 16,000 streetlights in largely quiet residential areas.

Then it put others on timers, cutting in half the number of hours they were lit each evening on the theory that a little light is better than none.

Now, the city has embarked on the third phase of its energy-saving effort by replacing hundreds of existing streetlamps at intersections with new, super-efficient bulbs that cost less to operate and will last more than three times longer.

Signalized intersections are the focus of the latest effort because turning existing streetlights off isn't an option for safety reasons. It's also where the upgrades make the most financial sense.

"The energy bang for the buck is the highest at those locations," said Steve Kroeck, deputy director of field services for the transit and public works department.

Streetlights aren't metered like homes. The city pays on a per-pole basis depending on the wattage of the bulb. A 250-watt high-pressure sodium bulb found at many intersections, for example, costs the city $146 a year to operate.

But the new, 150-watt induction bulbs replacing them produce plenty of light but cost $74 annually, a nearly 50 percent savings, said John Miklaucic, a supervising electrical technician.

Total savings from the program isn't clear because the 775 new bulbs are still being installed, Miklaucic said. But whatever the figure, it's going to be worth it to the city because $400,000 in federal stimulus money paid for the new bulbs and the labor to install them.

"We wouldn't have done this on our own dime," Miklaucic said. "It just wouldn't have happened."

The new induction lights cost about $267 each and are similar to florescent lights. The key difference is they don't contain electrodes that need to spark each time the bulb is turned on. They often are referred to as electrodeless lamps. Instead, light is produced when the mercury vapor inside the lamp is excited by an electromagnetic field created by an inductor outside the bulb.

The light is whiter than that orange-tinted, high-pressure sodium bulbs the city has used for decades, Miklaucic said.

"I think that what catches people's attention most. The color difference is pretty astounding," he said.

Part of the $400,000 also is being used to buy and install 1,700 timers for existing lights. Once those are installed, the city expects to cut its $800,000 PG&E streetlight bill in half.

In addition to intersections, induction bulbs are being installed in some locations where it is labor intensive to replace bulbs when they burn out, explained Rick Moshier, director of the transit and public works department.

Parker Hill Road, a winding two-lane road in the Fountaingrove neighborhood, got them because it requires traffic control measures whenever crews have to replace burned-out bulbs, Moshier said. The longer life of the new bulbs mean the city's workload should be reduced in future years.

The new lights, made in the U.S. by companies based in San Francisco and Irvine, are built to last 100,000 hours.

The goal of the city is to have about a third of its lights turned off completely, a third on timers and the balance replaced with the new induction lights, Kroeck said.

Once the signalized intersections are completed in a few weeks, the city will need to decide how aggressively to swap out the thousands of other lower-wattage streetlamps.

There is an argument to be made to aggressively replace them all, and some cities are doing just that, Moshier said. The benefits include lowering the city's greenhouse gas emissions.

But when local tax dollars are paying the tab, the cost-benefit analysis doesn't pencil out as well and phasing them in over time makes more sense, he said.

"We don't need to a tizzy and do it all in one year," Moshier said.

You can reach Staff Writer Kevin McCallum at 521-5207 or kevin.mccallum@pressdemocrat.com.