Night Sky, LEDs and Landscape Lighting

Richard Wainscoat, University of Hawaii, Institute for Astronomy

If you live on Oahu, you may have looked up at the night sky recently, and wondered where all the stars have gone. But if you live on the neighbor islands, you’ve probably seen the night sky in all its magnificence, and on a moonless night, gazed at the Milky Way — the galaxy in which we live.

At the University of Hawaii, we are now finding that more than half of our undergraduate students have never seen the Milky Way. The number of young people who have never seen the Milky Way is growing rapidly, and an entire generation of children is now growing up without seeing a dark night sky. Artificial light is making the night sky bright. Much of this problem is avoidable. Excessive, misdirected or obtrusive light is often referred to as light pollution.

There are two processes that make the night sky bright. Air molecules in Earth’s atmosphere scatter urban light downwards. This scattering is strongly color dependent — blue light scatters the most — and is the reason why the daytime sky is blue, and sunsets are red. Aerosols, such as particulates from Kilauea when we have southeast winds, also scatter urban lights and make the sky bright. On voggy nights, on Oahu, the night sky is very bright, and it may only be possible to see only a few of the brightest stars.

Hawaii is home to two of the best astronomical observatory sites on the planet: Mauna Kea on the Island of Hawaii, and Haleakala on the Island of Maui. Artificial lighting harms everyone’s ability to view the night sky, and is particularly harmful to the large telescopes at these observatories. Light pollution is also harmful to many animals, including endangered birds and turtles, and is also harmful to human health. Both Hawaii and Maui Counties have lighting ordinances in place to protect the dark night sky. The lighting ordinance in the County of Hawaii is presently being revised. Kauai has endangered birds that are severely affected by unshielded lights. State law places strict limitations on shoreline lighting across the entire state.

Proper shielding of lights is the most effective way to reduce light pollution. The high level of light pollution on Oahu, compared to the neighbor islands, occurs partly because there are more people on Oahu, but the lack of proper shielding on much of the lighting on Oahu is a major factor. In contrast, most of the lighting in Hawaii, Maui, and Kauai counties is properly shielded.

The lighting industry is presently undergoing a major transformation coming from the increasing maturity of lighting from Light Emitting Diodes (LEDs). Over the next 10 years, we can expect most lighting to be replaced by LEDs. A few years ago, salesmen were peddling blue-rich LEDs for their energy efficiency. These “cool white” LEDs cast an ugly colored light that some have referred to as prison lighting or zombie lights — not something most people would choose for landscape lighting. Over the last few years, the energy efficiency of warmer colored LEDs (that have less blue light and more yellow, orange and red light) has improved dramatically. Most people prefer the color of warmer colored lighting at night.

Fortunately, warmer colored lighting is less harmful to the night sky, is less harmful to endangered species, and is less harmful to human health, so the more aesthetically pleasing colors are also more environmentally friendly.

Early adopters of LED lighting who installed cool-white LEDs should consider replacing them with warmer colored LEDs to improve energy efficiency and aesthetics, and to reduce their impact on the environment. When choosing outdoor lighting, correlated color temperatures (CCT) of 2700 K or below should be chosen if white lights are being used. Amber LEDs and filtered LEDs have lower environmental impacts and may be used instead of white LEDs.

Landscape lighting in the Counties of Hawaii, Maui and Kauai should be fully shielded. This means that no light should be emitted in the horizontal plane above the light fixture. In these locations, the amount of light that is used should be minimized — this means that lighting with good optics should be selected. The light should be directed only onto the area that is to be illuminated, and not sprayed elsewhere (where it is not needed or wanted). Selection of light fixtures with good optics, and limiting the amount of light to only what is needed, will produce significant energy savings.

Landscape lighting on the Island of Hawaii must be turned off by 11pm. Unshielded landscape lighting in Maui county must also be turned off by 11pm. Limiting the duration of lighting also saves energy. LEDs can also be easily dimmed. There are excellent examples of beautiful landscape lighting that conforms to the lighting ordinance at some of the hotels on the Island of Hawaii.

Landscape lighting can coexist with preserving our view of the night sky, and with the other environmental considerations, but only if it is done carefully. Proper shielding is critically important, as is careful choice of the spectrum of the light. For many reasons, blue light is bad — choose warmer colored lights. Lighting laws must be followed in Hawaii and Maui Counties, and near the shoreline everywhere in Hawaii. The endangered birds on Kauai mean that proper shielding is mandatory in the County of Kauai.

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About the author  ⁄ Garrett Webb

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