We are privileged in Northern New Mexico to enjoy the glories of the night sky. Seeing the Milky Way on a clear summer night is a common experience for us. But our growing population and our tendency to use more light than we need in public places threaten our beautiful skies. The light we use, so necessary to our lifestyles, spills out and up into the night sky.

The International Dark-Sky Association has recently recognized Valles Caldera National Preserve as an International Dark Sky Park, joining several other units of the National Park Service in our state. These and other dark sky sites are highlighted by New Mexico’s Tourism Department for their value to casual stargazers and astronomers.

But the problem of light pollution is bigger than stargazing. Artificial lighting adversely affects wildlife, perturbing their diurnal cycles, just as our encroachment on habitat endangers their survival.

Our human diurnal cycles are also ill-affected by overlighting the night. At night we are most comfortable with what we refer to as “warm” lighting: the light of a fireplace or candles, or a soft incandescent bulb. Light that is too bright, or too blue, as in office settings, causes glare and hinders rest.

The color of lamps is expressed in terms of their “color temperature” in degrees kelvin (K). Counterintuitively, a lower-color temperature corresponds to what we call “warmer” light. The orange flame of a fireplace has a color temperature of about 1400 K, an incandescent bulb or high-pressure sodium lamp about 2700 K, a fluorescent light in a typical office about 4000 K, and the midday sun, 5600 K. The higher the color temperature, the greater the amount of blue light emitted. Since blue light is more effectively scattered and reflected than red light, higher-color temperature lamps produce more light pollution, glare and skyglow, even when properly shielded.

For several decades, the streets in our major cities, including Santa Fe, have been lit by 2700 K high-pressure lamps. These are the standard for safe street lighting. Because reflected or scattered blue light causes glare, 4000 K street lamps are less safe than 2700 K lamps.

The city of Santa Fe wants to replace its high-pressure sodium street lamps with LED lamps having color temperatures of 3000 K and 4000 K. This plan is a grave mistake. It would reduce safety and turn charming Santa Fe into the most garishly lit city in our region. Flagstaff, Ariz., comparable in size to Santa Fe, and Tucson, Ariz., a much larger city, both forbid street lamps of color temperature above 2700 K.

The International Dark-Sky Association (darksky.org) recommends street lighting with color temperature of 2700 K or less, for the benefit of night sky protection, wildlife protection and human health. The American Medical Association recommends “the use of 3000 K or lower lighting for outdoor installations such as roadways” (see bit.ly/2ZCRz30).

A meeting of the City Council to discuss this lighting project is scheduled for Wednesday. I urge all interested parties to show up and make their voices heard. Santa Fe must be deterred from this error.

Galen Gisler is a scientist and New Mexican whose love affair with the night skies began in his childhood.

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