Industry News




 

01/18/2013

LED: New Material, New Possibilities?

 
New possibilies for LED lighting may make the technology more applicable to traditional lighting applications.

Heard about FIPEL?  Well, it looks like LED may have new possibilities as well.  LEDs are known for their energy efficiency and durability, but the bluish, cold light of current white LEDs has precluded their widespread use for indoor lighting.

Now, University of Georgia scientists have fabricated what is thought to be the world's first LED that emits a warm white light using a single light emitting material, or phosphor, with a single emitting center for illumination. The material is described in detail in the current edition of the Nature Publishing Group journal "Light: Science and Applications."

"Right now, white LEDs are mainly used in flashlights and in automotive lamps, but they give off a bluish, cool light that people tend to dislike, especially in indoor lighting," says senior author Zhengwei Pan, an associate professor in the department of physics in the UGA Franklin College of Arts and Sciences and in the College of Engineering. "Our material achieves a warm color temperature while at the same time giving highly accurate color rendition, which is something no single-phosphor-converted LED has ever been shown to do."

Two main variables are used to assess the quality of artificial light, Pan explained. Correlated color temperature measures the coolness or warmth of a light, and temperatures of less than 4,000 kelvins are ideal for indoor lighting.

Correlated color temperatures above 5,000 kelvins, on the other hand, give off the bluish color that white LEDs are known for. The other important measure, color rendition, is the ability of a light source to replicate natural light. A value of more than 80 is ideal for indoor lighting, with lower values resulting in colors that don't seem true to life.

The material that Pan and his colleagues fabricated meets both thresholds, with a correlated color temperature of less than 4,000 kelvins and a color rendering index of 85.

Warm white light can commonly be achieved with a blue LED chip coated with light emitting materials, or phosphors, of different emitting colors to create what are called phosphor-based white LEDs, Pan said. Combining the source materials in an exact ratio can be difficult and costly, however, and the resulting color often varies because each of the source materials responds differently to temperature variations.

"The use of a single phosphor solves the problem of color stability because the color quality doesn't change with increasing temperatures," says lead author Xufan Li, a doctoral student in the College of Engineering.

To create the new phosphor, Pan and his team combine minute quantities of europium oxide with aluminum oxide, barium oxide and graphite powders. They then heat the powdered materials at 1,450 degrees Celsius (2,642 degrees Fahrenheit) in a tube furnace. The vacuum of the furnace pulls the vaporized materials onto a substrate, where they are deposited as a yellow luminescent compound. When the yellow luminescent compound is encapsulated in a bulb and illuminated by a blue LED chip, the result is a warm white light.

Although his team's results are promising, Pan emphasized that there are still hurdles to be overcome before the material is used to light homes, businesses and schools. The efficiency of the new material is much lower than that of today's bluish white LEDs. Scaling the production to an industrial scale will be challenging as well, since even slight variations in temperature and pressure in the phosphor synthesis process result in materials with different luminescent colors.

The new yellow phosphor also has a new lattice structure that has not been reported before. The researchers currently are working to discern how the ions in the compound are arranged in hopes that a better understanding of the compound at an atomic level will allow them to improve its efficiency.

"We still have more work to do," Pan says, "but the color temperature and rendition that we have achieved gives us a very good starting point."

 

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Our mission is to help our customers manage their buildings' energy costs, improve reliability, and enhance performance while having a positive impact on the environment.
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Mitsubishi Electric’s H2i R2-Series heat pumps provide 100% heating capacity down to 0° F and simultaneous heating and cooling down to -4° F delivering year-round comfort, regardless of climate zone.

 
04/23/2014

A key part to curbing emissions is working with local and city officials, tenants, and other groups to help make entire communities more sustainable. BOMA International shares the following strategies for greening your facility and community.

04/21/2014

Lighting fixes target the bottom line.

04/16/2014

The U.S. Army plans to start development of a solar array that will provide about 25% of the annual installation electricity requirement of Fort Huachuca, Arizona.

04/15/2014

The EPA's annual greenhouse gas emissions report is now available.

04/14/2014

Are you what some would call a “climate-change denier”? If so, you'll want to read this.

04/10/2014
Los Angeles has remained the top city for ENERGY STAR certified building since 2008, while Washington, D.C. continues to hold onto second place for the fifth consecutive year, according to a new list released by the EPA.
04/09/2014
Green construction has grown massively over a short period of time.
04/07/2014
Field demonstrations of newly proven energy-efficient technologies are yielding valuable results for the U.S. Navy, helping it meet energy goals.
04/03/2014
Building owners in Chicago now have more options when it comes to getting their building energy data verified.
04/01/2014
According to a new report from Eaton, such outages are up 15% in 2013 over 2012 and over half of those surveyed believe that downtime could have been prevented.
03/31/2014
The newly revised ANSI/ASHRAE Standard 105-2014, Standard Methods of Determining, Expressing, and Comparing Building Energy Performance and Greenhouse Gas Emissions, aims to provide a consistent method of measuring, expressing, and comparing the energy performance of buildings.
03/27/2014
Facility managers face an every expanding array of sustainability choices and challenges, but for the next generation of FMs, green practices could be second nature as sustainability literacy enters the K-12 school system.
03/25/2014
While the economic recession explains the decline in sales in 2008 and 2009, it is much less clear why sales have continued to fall.
03/24/2014
University of Washington (UW) scientists have built the thinnest known LED that can be used as a source of light energy in electronics.
03/21/2014
Mississippi Governor Phil Bryant signed Senate Bill 2378 into law, effectively enacting the state’s first building code.
03/19/2014
In an attempt to improve building energy performance, the DOE’s National Renewable Energy Laboratory has released a web-based tool called the Technology Performance Exchange, or TPEx.
03/18/2014
Could green building practices pose unanticipated life-safety hazards?
03/13/2014
Worried about workplace violence in your facility? Researchers have discovered that “mindfully observing” high-risk employees can avert danger and workplace violence.
03/11/2014
Through the DOE’s Building Energy Codes Program, every dollar the DOE has spent on building energy codes over the past two decades has resulted in $400 in energy cost savings.
03/07/2014
It is possible to harvest energy from Earth's thermal infrared emission into outer space, according to new research from the Harvard School of Engineering and Applied Sciences.
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