Questions about street lighting and the environment

What is the best color temperature for not disrupting plants?

To avoid disrupting the life-cycle of plants we have to worry about both the plants and also the pollinators – insects, birds, bats, etc. – that propagate the plants. It’s a “whole ecosystem” effect. 

Many plants – including some cactus and other plants in our part of the desert southwest – bloom only at night. The night blooming cereus (Queen of the Night) cactus is one example. Too much artificial light at night disrupts this plants ability to propagate. 

Another example is the agave. It is pollinated at night by bats, which avoid light entirely. No dark night, no bats, no agave (and no tequila). 

The principal affect in all cases is from the light itself; so, it is important to keep the light levels as low as possible. Some plants are more strongly affected by higher color temperature (bluer) lighting; others, by lower color temperature (redder) lighting. Insect pollinators are generally much more strongly disturbed by higher color temperature (bluer) lighting than by lower color temperature (redder) lighting. [Think about those “bug-zapper” accessories, which attract bugs by using a very strong blue-violet light.] Bats, also, are more seriously disturbed by higher color temperature lighting than by lower color temperature lighting. 

What is our current horizon loss due to light pollution? How will the city’s plan affect this?

The answer depends on how far you are from Santa Fe when you look toward it, the presence of any low lying clouds over or between you and the city, and the amount of moisture or dust in the atmosphere. From the Eldorado area on U.S.285 the Santa Fe light dome on a good night is about 10 -15 degrees in height; on a bad night it may reach as high as 40 degrees. Proper shielding and adjusting lighting levels so they are ore in line with IES recommendations will reduce the size of the light dome. On the other hand, increasing light color temperature (as measured in Kelvins ) will increase the dome.

You can see a picture of the Santa Fe light dome as viewed from Eldorado here.

For a different view, on our home page scroll down to find a graphic produced from satellite data showing the intensity of light from the Santa Fe area as seen from space. ALL the light in that picture is wasted light: none of it helps us on the ground. 

What are the effects of light pollution and color temperature as it affects our ability to star-gaze?

How do “lumens” affect dark skies?

Any light directed upward will affect our skies, making it more difficult to star-gaze. Upward directed light includes light from improperly shielded streetlights. It includes light reflected off of the the street or parking lot pavement, or sidewalks. It includes light reflected off of buildings that incorrectly illuminated. 

For the same lumen of lighting, light of higher color temperature has a greater effect on our ability to star-gaze than does light of lower color temperature. This is because light of higher color temperature scatters more as it passes through the atmosphere. [You can read more about scattering at the question “I would also like to hear more about scatter of light due to temperature, please.“]. Scattered light creates sky-glow, which decreases our ability to observe stars. 

To preserve our dark skies we need to keep the total lumens, across all city street lights, as low as is consistent with public safety; and, we need to keep the color temperature of the lighting (“Kelvin”) also as low as possible.