Yellow Stands for Caution in Converting Street Lights

Maybe the reason that the idea of replacing San Diego’s yellow-cast street lights with whiter, high-pressure sodium lights keeps coming up is because the city of San Diego cannot afford what it really needs: more police officers.

But converting the lights would be ill-advised for many reasons:

* The conversion would cost $4 million to $8 million and take up to six years.

* Operating and maintaining the new lights would run about $430,000 more a year. The high-pressure lights use more energy.

* More energy translates into more air pollution.

* High-pressure lights are more prone to vandalism and, although they last longer, the light they put out declines with age.

* The whiter light that high-pressure sodium puts out interferes with the work of astronomers at Mt. Palomar and Mt. Laguna observatories. Yellow light can be mostly filtered out. Whiter light, which contains many colors, competes with the faint light from the far reaches of the universe.

There might be some argument for accepting those disadvantages if there was any proof that high-pressure sodium lights were effective in reducing crime. But there isn’t.

Colors are truer under high-pressure sodium lights, which have a pink-amber color that appears whiter. The yellow cast of low-pressure sodium lights washes out color. But watt for watt, high-pressure lights are no brighter than low-pressure lights.

So, even if the city were to replace the lights that help keep a major observatory functioning, city streets would be no better lighted.

That would require using higher wattage, which might be warranted on streets where lights are far apart, or in high-crime areas. But the brighter lights should still be low-pressure sodium.

It would be a shame, after spending years installing low-pressure sodium lights for sound scientific and economic reasons, if the city were to spend millions converting back and then find that city streets were no safer.