Earlier this month, people around the world celebrated International Dark Sky Week. Here, in New Mexico, we can often see the Milky Way on a clear summer night. 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.
Human diurnal cycles are also ill-affected by over-lighting 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 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 an office about 5000 K, and the midday sun 5900 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 K lamps produce more light pollution, glare and skyglow, even when properly shielded.
For several decades, the streets in our major cities, including Albuquerque and Santa Fe, have been lit by 2700 K high-pressure lamps. These are the standard for safe street lighting.
Albuquerque replaced high-pressure sodium streetlights several years ago with lamps that emit at the higher/bluer end of the range, increasing light pollution and glare. A project in the works to install lights on the city’s West Side has attracted little interest from proponents of dark skies.
The City of Santa Fe also wants to replace its high-pressure sodium streetlamps with LED lights. Dark sky advocates in this city are working with the mayor and council. They hope to dissuade officials from installing lamps with color temperatures of 3000 K and greater. Installing these lights with high Kelvin numbers would reduce safety and turn charming Santa Fe into one of the most garishly lit city in our region. Flagstaff, Arizona, comparable in size to Santa Fe, and Tucson, Arizona, a much larger city, both forbid streetlamps of color temperature above 2700 K.
Progress is being made across the state to preserve New Mexico’s night skies. However, it is important for people in every community, large and small, to become involved as more development occurs and as older streetlights are replaced with LEDs.
Galen Gisler is a scientist and native New Mexican whose love affair with the night skies began in his childhood.