The Color of the Night Sky is Changing

Red is the new Black

August 2, 2012

In cities, clouds scatter artificial light back down towards the ground, drastically increasing the sky brightness. In natural areas, clouds make the sky darker.
 ( — The colour of night-time skyglow may be about to undergo a radical change worldwide, according to scientists of the Freie Universität Berlin and the Leibniz Institute of Freshwater Ecology and Inland Fisheries. They predict that with increasing use of LED street lamps, the colour of the night sky will become bluer. To track this change, the researchers developed a prototype measurement device, and used it to show that the sky currently contains far more red light on cloudy nights compared to clear nights. Their report, entitled “Red is the New Black”, is published in the journal Monthly Notices of the Royal Astronomical Society.
Christopher Kyba, physicist at the Freie Universität and lead author of the study, explains that innovations in lighting technology will result in changes in the colour of streetlights. “The current worldwide trend of replacing gas discharge lamps with solid state lighting, such as LEDs, will affect the radiance and spectrum of urban skyglow.” In order to understand the potential impacts of this change on ecology, it will be essential to monitor the sky over the long term. The scientists used the new instrument to study how clouds affect sky brightness in urban areas. “For almost all of evolutionary history, clouds made the night sky darker, just like they do in daytime”, said Franz Hölker, ecologist at the Leibniz-Institute of Freshwater Ecology and Inland Fisheries, study author, and leader of the project “Verlust der Nacht” (Loss of the Night). In areas with artificial light the effect of clouds is now reversed, and the size of the effect depends on colour. The researchers found that in Berlin the blue portion of skyglow is 7 times more radiant on cloudy nights than on clear, and 18 times more for the red part. In the visual range used by most animals, the authors say that cloudy skies are now thousands of times more radiant near cities than they were throughout most of history. They expect that the addition of this extra light affects predatory-prey relationships where the predator hunts using vision, for example between owls and mice. The sky is blue in daytime because the cloud free atmosphere is very good at scattering short wavelength light. The scientists therefore express concern that unless special care is taken in design and implementation, a switch to whiter LED lights could make the sky much brighter on clear nights. They suggest that cities that have decided to change to solid state lighting should purchase lamps that emit no upward light, and use “warm white” lights with as little blue light as possible. The research was funded by two interdisciplinary projects, MILIEU and “Verlust der Nacht”. The “Verlust der Nacht” project, funded by the German Ministry of Education and Research (BMBF), is specifically devoted to quantifying light pollution and investigating its impact on humans and the environment.

LED Lights — Green Power

Alternative LED Lighting Combats Energy Crisis

Jacob Gersh, DOE ARPA-E
Date: 11 November 2011 Time: 11:17 AM ET

behind the scenes, bts, national science foundation, nsf, LED, LED lighting, light, energy, downlights, Cree TrueWhite technology, Cree LED Lighting, Jacob Gersh, ARPA-E, led lighting versus fluorescents, led lighting versus traditional, what's good about
Cree LR6 LED downlights illuminate the dining room of a Denny’s restaurant in Colorado Springs, Co. More than 400 LR6 downlights were installed in the dining rooms five area restaurants, cutting approximately $15,500 per year in energy costs
CREDIT: Cree, Inc.

This Behind the Scenes article was provided to LiveScience in partnership with the National Science Foundation.

Alternative lighting is emerging as a potent method to combat the energy crisis. Light-emitting diode lighting technologies could provide an innovative way to save energy and make wasteful lighting obsolete.

Cree LED Lighting is manufacturing such a technology in Durham, North Carolina. Cree focuses on the production of light-emitting diode (or LED) lighting, powerand communications devices, all of which are supported by advancements in silicon carbide semiconductor technology.

Silicon carbide chips are more durable and perform better than traditional silicon semiconductors. Cree discovered these properties of carbide chips while working with the University of Arkansas in 2001 on a grant from the National Science Foundation. They designed computer modeling methods to simulate silicon carbide semiconductors under extreme conditions. Cree then worked on a 2007 National Science Foundation grant to develop microwave technology to rapidly process silicon carbide semiconductors.

LEDing the way

Although Cree’s work led to semiconductor applications for power and radio technology, Cree’s most successful products to date are LED lights using their silicon carbide semiconductors.

If widely adopted, the potential impact of LED lights on national energy consumption could be enormous. “On average, LED lighting can save up to 85 percent of the electricity used by incandescent bulbs, since most of the energy emitted from those lights is converted to heat instead of light,” said Michelle Murray, Director of Communications at Cree. “For fluorescents, depending on whether you compare LED lighting to compact fluorescents or fluorescent tube lighting, LEDs can save between 20 and 50 percent of the energy used by those lighting sources.”

In addition to LED lighting’s energy benefits, it holds mechanical advantages over standard fluorescent and incandescent lights.

“LEDs do not have fragile filaments like incandescent bulbs, or special gases inside, like fluorescents,” said Murray.

The best choice

The filaments in most incandescent bulbs not only limit each bulb’s life, they can generate large amounts of waste heat. Fluorescent bulbs are more efficient than incandescent bulbs, but contain potentially harmful mercury. When fluorescent bulbs expire, the toxic mercury has to be properly managed in order to protect both human health and the environment.

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Cree’s CR6 LED Energy Star certified downlight powered by Cree TrueWhite technology.
CREDIT: Cree, Inc.

“Any lighting system is only as good as its weakest part,” said Murray. “So good quality solid-state lighting [like LED based bulbs] has a system-level design approach — the LEDs, the optics, the driver and the thermals are all optimized for their specific application. This allows LED lighting to last for years — even decades.”

LED lights are not given a lifetime based on failure, like incandescent or fluorescent bulbs. Instead, LED lights are considered in need of replacement when they only provide 70 percent of their original efficacy. The LED technology developed by Cree is engineered to last a minimum of 50,000 hours before requiring replacement, which is greater than the 40,000-hour lifetime of many fluorescent bulbs.

Failing fluorescents

Fluorescent bulbs are given an estimated lifetime based upon the failure rate of the bulb: After 40,000 hours of use, 50 percent of fluorescent lights will have broken and will require replacement. According to the DOE Caliper 9 Summary Report, because of that high failure rate, some fluorescent bulbs are advertised at a more practical lifetime of 24,000 hours — less than half the lifetime of a silicon carbide semiconductor-based LED.

In June 2011, President Barack Obama visited Cree to tour the company’s Durham, N.C. manufacturing facilities as well as meet with the Jobs and Competitiveness Council to discuss the direction of American business. The President highlighted Cree technology as a driving force in leading a clean energy revolution and aiding American manufacturing, but LED lighting is still not yet a familiar technology to the public.

“Awareness is the biggest challenge,” Murray said. “Awareness about how to buy good quality LED lighting products, and awareness that they already are on the market.”

Murray also highlights challenges in educating the public to understand the up-front cost of LED lighting versus the potential payback over the life of a fixture. Initially LED lights cost more than fluorescent and incandescent bulbs, but the savings in energy and bulb replacement typically pay for the LED’s higher cost over time.