Streetlights in Los Altos are undergoing an upgrade this month as PG&E replaces high-pressure sodium bulbs with light-emitting diode bulbs.
The modern lights cost less to operate and are supposed to last longer. They expend less than half the energy required by the older style of bulb, and PG&E estimates the upgrade will save Los Altos approximately $12,000 next year.
“The city is pursuing this because it is the right thing to do environmentally and economically,” said Erica Ray, Los Altos’ public information coordinator. “While PG&E does own the streetlights, we have a say in what happens to them.”
Although the city weighed in on the conversion to LED bulbs, PG&E is funding and implementing it; the utility company owns and maintains 525 streetlights in Los Altos. The bulb-swapping process is expected to take approximately 10 minutes per lamp fixture.
The directionality of the new bulbs is intended to distribute light more effectively, improving visibility for pedestrians and drivers.
While their brightness can more effectively illuminate a street, the LEDs’ color raised concerns in some of the first communities to receive the new bulbs, which have spread across the Bay Area in recent years.
Los Altos officials said they asked PG&E to install lights with a warmer color temperature in residential neighborhoods, reserving the brightest bulbs for commercial districts and thoroughfares.
As light-bulb technology has evolved, three different measures have come to qualify a light’s appearance and power consumption. Wattage measures the amount of electrical power a light bulb consumes, but also once provided a convenient sense of how much brightness to expect.
As fluorescent and LED bulbs became increasingly common – and could provide far more light per watt than older incandescent bulbs – a different measure, lumens, more effectively described a bulb’s brightness. Lumens measure the total quantity of visible light emitted from a source. Los Altos streets currently have 70-watt high-pressure sodium bulbs, with an output of 5,800 lumens. The new LEDs will use 28-watt bulbs to generate 3,300 lumens.
A third gauge, color temperature, measures the color of light emissions on a spectrum ranging from warm (more yellow) to cold (more blue/white), and is measured in kelvin. A flickering candle might cast 1,900 kelvin, while direct sunlight streams in at closer to 4,800 kelvin. Los Altos’ residential neighborhoods will get LEDs with a color temperature of 3,000 kelvin, the maximum recommended by groups such as the American Medical Association for nighttime illumination. Commercial areas will have 4,000-kelvin LEDs, which are expected to provide better visibility in high-traffic areas but have been associated by some critics with sleep disruption and light pollution.
Mountain View installed 2,200 new LED bulbs across the city last year, city communications coordinator Shonda Ranson said, all of which were 4,000 kelvin.
“Most residents were happy because they were much more effective for illumination,” she reported. “Because we chose a Dark Sky-compliant solution, the few concerns we heard about light pollution and the one concern over disturbing owl hunting patterns were assuaged.”
The 3,000-kelvin bulbs being installed in Los Altos represent an advance in LED technology. Until recently lower-kelvin lights required more watts to provide an equivalent lighting level, but warmer light has become more efficient in modern bulbs.
“In Los Gatos, they implemented the 3,000-kelvin lights (in residential areas) and we’re hoping that it will work well for us as well,” Ray said.
“New LED streetlights provide a more natural-looking light, which will last up to four times longer than HPSV bulbs,” PG&E senior manager Don Hall wrote in a letter to residents.