Electronic Design

Power LEDs Promise Brighter, More Cost-Effective Lighting

The votes are in, and readers have selected Cree’s XR-E series power LEDs as the most significant Leapfrog technology story of the year (see “White Power LED Lights The Way With A 160-Lumen Output,” Nov. 16, 2006, p. 39). And Cree has come a long way in improving the XR-E series since that story broke.

Improvements in the die, packaging, and materials have led to the company’s Cool series. These lights are “a more efficient version of the XLamp series and exhibit good color stability over the LED’s lifetime,” says Deb Lovig, Cree’s Program Manager for the firm’s LED City Initiative.

COOL SPECS
The lamp now produces a cool white light output of up to 250 lumens—a 56% improvement. It’s available in a cool white output (5000K to 10,000K color-corrected temperature, or CCT) with up to 114 lumens at 350 mA with an efficacy of over 90 lumens/W.

Also, Cree developed its Warm series for general use in indoor lighting, though it’s being used overseas for outdoor applications as well. Neutral and warm white versions (3700K to 5000K CCT) with outputs with up to 80.6 lumens at 350 mA feature an efficacy of up to 67 lumens/W, the same efficacy and color temperature of a compact fluorescent lamp (CFL).

“These are the best results reported for packaged, high-power LEDs,” says Paul Scheidt, product manager for Cree’s solid- state lighting products. The National Institute of Standards and Technology (NIST) has verified the results.

The white power LED chip is produced on a silicon-carbide (SiC) substrate that has an indium-galliumnitride (InGaN) epitaxial layer grown on it. The reflow-soldered surfacemount chip features a small footprint of 7 by 9 mm (Fig. 1).

Solid-state light sources are more efficient and have longer lifetimes than conventional light sources. They don’t require much maintenance either, making them a cost-effective alternative for a number of general illumination and back-lighting applications. As a result, applications are spreading quickly in office buildings, parking lots, outdoor and indoor lighting, auto headlights, garage and warehouse low-bay illumination, camera-flash and projection displays, and even flashlights.

In fact, LED lighting has made the parking lot and lobby at Cree’s headquarters in Durham, N.C., a lot brighter (Fig. 2). More and more lighting fixture manufacturers are using Cree LED light sources in their products for use in industry and the home.

ON THE STREETS
According to the U.S. Department of Energy (DOE), 22% of electricity used in the U.S. powers lighting. The DOE claims that in the next 20 years, rapid adoption of LED lighting in the U.S. can reduce electricity demands from lighting by 62%. Also, it could eliminate 258 million metric tons of carbon emissions. It could prevent the building of 133 new power plants. And, it could result in financial savings that could exceed $115 billion.

Proof of this is the LED City initiative. Toronto, Ann Arbor, Mich., and Raleigh, N.C., have joined this expanding organization of government and industry parties working to evaluate, deploy, and promote LED lighting technology across the full range of municipal infrastructures. Its goal is to save energy, protect the environment, reduce maintenance costs, and provide better light quality for improved visibility and safety.

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“We believe the cost savings and benefits of LED lighting are real and achievable today,” says Charles Meeker, mayor of Raleigh, which was the first municipality to sign on with LED City.

Considering initial costs and energy savings and maintenance savings, the City of Raleigh estimates it would achieve a payback for its lighting investment in seven years. It has calculated that an initial investment of $42,300 balanced by electricity savings of $2803 per year and maintenance savings of $3325 per year, each increasing 3% per year, would yield this payback time span. These projections were developed in May for a pilot lighting project for the city’s municipal garage.

“LED power lamps are still relatively more costly than conventional light sources when first purchased, but that price difference is narrowing,” says Scheidt. “Our goal is to establish that over the long term, LEDs are more cost effective because they have longer lifetimes, less maintenance requirements, dissipate less energy and are more energy efficient, and contribute greatly to an eco-friendlier environment.”

For example, the City of Ann Arbor, which will install more than 1000 LED streetlights over the next two years, is projecting a 50% savings in energy and a 3.8-year payback on its initial investments in solid-state lighting. It believes that full implementation of LEDs in the city will cut public energy use in half and reduce greenhouse emissions by 2425 tons of carbon dioxide annually, the equivalent of taking 400 cars off the road for a year.

“Our investment is based on three years of extensive research on the energy and maintenance savings associated with LED lighting, citizen surveys, and a very successful pilot project of using 25 LED lights spanning an entire city block,” says Ann Arbor mayor John Hieftje.

The City of Toronto has the same rosy outlook. Led by the Toronto Association of Business Improvement Areas (TABIA), the city’s use of LEDs over the past four years has evolved from holiday light exchanges to retail displays and streetlight installations.

“Within the next 10 years, you’re going to see streetlights all over Toronto either converted or in the process of being converted to LED lighting because LED lights will reduce the energy consumption by 50% or more,” says Toronto deputy mayor Joe Pantalone. “It will save the taxpayers money and save the environment.”

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