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Educational November 2018

The shifting color of the outdoor lighting revolution

High-intensity LEDs emit a large amount of blue-white light that creates glare on the roads, disrupts species that need a dark environment, and can even affect circadian rhythms while we sleep—but technology is shifting LED color temperature toward a warmer outlook.

LEDs have proven their capabilities for applications from car headlights and bicycle lights to Christmas lights and lamps inside your home. When it comes to outdoor lights, LEDs have revolutionized the industry: they last twice as long as high-pressure sodium bulbs and they save energy. And saving energy means a decrease in fossil fuel usage as well as significant cost savings for municipalities, corporations, and residents that require a well-lit space.


Although they are more efficient than high-pressure sodium lights and other older outdoor lighting technology, LEDs have not been a perfect solution for saving energy and money: the light quality this technology offers has been called unpleasant at best, and hazardous at worst. The good news? Newer LED iterations are poised to change that.

How LEDs work


Let’s start at the beginning. What makes LEDs efficient? It all comes down to how they produce light. An individual LED will emit only one color, making these lights perfect for applications like red traffic lights or yellow warning signs; however, it’s more complex to produce white light. The cheapest, most efficient color to produce is blue because of its short wavelength, which requires a smaller amount of energy to produce light in comparison to colors like orange, which have a longer wavelength and require more energy.


To create white light, the cheapest and most efficient way is to start with a blue LED; the blue LED shines onto phosphors that absorb some of the blue light and emit yellow light. When the yellow light combines with the remaining blue light from the LED, the result appears white.


The shade of white will depend on the blend of yellow and blue. This shade is measured on the color-temperature scale, measured in Kelvins. The blue-white light that LEDs produce comes in at about 4500 to 6500K. In comparison, “warmer” color temperatures of 2700 to 3000K are generally what we’re used to inside our homes, with an orange-yellow hue that is similar to the high-pressure sodium lighting that was once ubiquitous on our streets.

The rise of the LED street light


Cities across the United States have replaced their high-pressure sodium lights with LED outdoor lights—about 5.7 million of them. Consultant firm Navigant released a report in July 2015 estimating that if all remaining non-LED outdoor lighting in the US were switched to LEDs overnight, the country could save about 662 trillion British thermal units—enough energy to power 5.8 million average homes in the US for an entire year.


Many cities have reaped the savings benefits of the swap. For instance, Los Angeles replaced nearly 174,000 street lights for an energy savings of about 64%, reducing CO2 by 62,000 metric tons per year—the equivalent of about 66 million pounds of coal (and reducing coal production can help reduce cases of asthma, lung cancer, and congestive heart failure). Since the lights were installed in 2009, they have saved approximately $9.3 million annually in energy costs and around $2.5 million in maintenance costs.


Meanwhile, all of New York’s 250,000 lights are being replaced with energy-efficient LEDs, with an estimated $6 million in energy savings and $8 million in maintenance savings per year. Seattle, Boston, Detroit, San Francisco, Houston, and many more smaller cities have also transitioned from high-pressure sodium to LED bulbs.


However, some vocal citizens in cities that have installed LEDs have expressed concerns about how bright the lights are. In Davis, California, 650 lights installed in May 2014 were replaced only a few months later, at a cost of $350,000. In Montreal, Canada, 132,000 high-pressure sodium street lights are in the process of being replaced with 3000K bulbs instead of 4000K, except in main thoroughfares; luckily, the decision was made before the $110 million conversion began. Pushback has also happened in cities like New York and Seattle, with mixed results. Some cities have chosen to stick with their chosen color temperature, while public pressure has forced others to replace the bulbs with warmer lights.

Got the LED blues?


The discomfort of these bright lights is not without scientific backing. While LED technology has clearly saved a lot of money in many municipalities, it may have done so to the detriment of residents’ health.


In the past decade or so, experts have studied the effects of light on human health, wildlife, and even the view of the night sky. Since human eyes are more sensitive to blue and green light than yellow or orange light, we experience more discomfort from the glare of unshielded blue light—think of those newer LED headlamps of oncoming traffic shining in your eyes—than we do from more amber-hued lights.

In fact, too much blue light in the evening can disrupt sleep, suppressing production of melatonin, the hormone that induces sleep. Just like looking at the blue light of a cell phone screen before bed can disrupt your sleep, so too can light from a blue-hued street light outside your bedroom window.


According to the American Medical Association (AMA), white LEDs impact circadian sleep rhythms five times more than the orange-hued color of conventional street lights. In a 2016 press release, the AMA reported that “recent large surveys found that brighter residential nighttime lighting is associated with reduced sleep times, dissatisfaction with sleep quality, excessive sleepiness, impaired daytime functioning, and obesity.”

Other studies have shown that white street lights may contribute as much as four times the nighttime sky glow that an orange-hued high-pressure sodium light of the same lumens would produce. As early as 2009, astronomers were criticizing LEDs as a cause of light pollution. And the International Dark-Sky Association, which opposes light pollution, worried the LEDs would affect both the night sky and the environment in general. Studies have shown the lights affect many species, including birds, insects, and other animals; for instance, newly hatched sea turtles have confused the bright-white street lights for the light of the moon, and headed inland rather than toward the ocean, dying in the hundreds of thousands each year on US beaches.


In 2016, the AMA adopted guidance for LED lighting, encouraging communities to “minimize and control blue-rich environmental lighting by using the lowest emission of blue light possible to reduce glare.” They also recommend the intensity of LED lighting should minimize blue-rich light, and that all LEDs should include proper shielding to minimize glare. They suggest considering using LED lighting that can be dimmed during off-peak times, like overnight.

Warmer LEDs on the horizon


What if LEDs could produce a warmer color temperature to meet the AMA’s lighting recommendations? As noted, more energy is required to make orange light; early iterations of LEDs with warmer color temperatures required a huge loss of lumens—that’s the amount of visual light they emit—to function compared to cooler lights. Essentially, blue lights around 5700K were much more efficient. But advances in technology have helped reduce this lumen loss, which used to be as much as 70%.


Today, LED lighting companies are producing fixtures that only lose 1% of their lumens to reach a warm color temperature of 3000K. To do this, some are adding a high-efficiency, red LED to the existing blue LED with the yellow phosphors, which is more energy efficient than simply using red-emitting phosphors. While blue light is not eliminated, it is reduced. And the light color temperature looks more like the original high-pressure sodium lights, while still providing the efficiency and long lifespan of the newer LED technology.


Other lighting companies are even able to achieve the 3000K color temperature without combining the red and blue LEDs, taking a more traditional approach to their engineering, which allows for reduced costs. This type of fixture is available for EverGen lighting systems. Unlike other outdoor lighting brands, which may only measure the bare LED’s output, Sol measures light output based on the fixture as well as the LEDs, making the light output we specify far more sustainable over the product’s lifetime. And with multiple lighting profiles available, dimming can be used intentionally and effectively to minimize light pollution during non-peak hours overnight.


The solar LED lighting revolution continues—and the warmer LEDs now available should offer an energy-efficient lighting solution that also minimizes health concerns and light pollution.


Learn more about the advantages of choosing our solar lighting in your community.

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