The lighting is on the wall: Solid state is threatening to dismantle the dominion of incandescent and compact fluorescent light (CFL) sources. Illumination applications based on solid-state lighting are slowly replacing those previously ruled by the older technologies. Though very expensive to use, solid-state lighting has proven more efficient and in sync in a world where government initiatives are calling for a greener environment and less energy consumption.
High-brightness white LED lighting systems, particularly for large-area displays, are the wave of the future. A well-designed LED light source uses about 10 to 12 W to produce 900 lumens of light output. Comparatively, an incandescent light bulb requires about 60 W. LEDs also can be dimmed, which will ease their transition into present-day incandescent light-bulb sockets.
Presently, the cost of using LEDs for general-purpose indoor and outdoor lighting remains high compared to incandescent and fluorescent light sources. However, the average selling price for a high-brightness LED has dropped in the last few years. That drop can be attributed to LED manufacturers using 4-in. wafers to make the devices, instead of the conventional 2-in. wafers. Even 6-in. wafers are under consideration for mass production.
A few notable white LED products on the market compete directly with halogen and metal-halide lamps up to 80 W, in terms of lifetime and energy savings, leading to lower costs. For example, the LEDtronics PAR38-12X12WF warm-white light and pure-white frosted soft flood bulbs operate from 85 to 265 V ac, require no special adapters, and consume less than 18 W for energy savings of 77% to 85% (Fig. 1).
Bridgelux, a solid-state lighting company, is adopting the slogan “penny per lumen” to make white LEDs more affordable for many applications. “We’ve been increasing LED chip performance some 15% to 20% every six months,” says Brian Fisher, director of corporate marketing. Bridgelux expects to produce 100-lumen/W cool white light sources that, when integrated into lighting fixtures, will turn the slogan into reality.
Luminus Devices Inc., a developer and manufacturer of highbrightness LEDs, calls its SBM-160 PhatLight LEDs the industry’s brightest multi-color LEDs available in surface-mount technology (SMT) packages. They’re aimed at architectural and entertainment applications that require high light output and high efficiency levels. Available in a four-chip package consisting of individual red, green, blue, and white LEDs that generate more than 1500 lumens combined, they use a high-performance ceramic substrate to achieve a thermal resistance of less than 1.5°C/W.
A NEW ERA Many expect LED illumination to revolutionize the lighting industry within the next five years (see “A Bright Future For LED Illumination”). That’s due to LED solid-state lighting’s efficiency edge over other light sources, and it’s one of the few illumination sources suitable for energy-efficient environments. Researchers are actively working on solutions for improved LED thermal-management methods, better color quality, higher lifetimes, and lower costs.
New global energy-conservation regulations are a driving force behind the adoption of LED lighting. In the U.S., the Energy and Security Act of 2007 restricts the sale of inefficient lamps. Europe is about to ban the clear 100-W incandescent lamp, followed by bans on other less efficient incandescent lamps. By 2012, the ban will be comprehensive.
China, which produces 70% of the world’s light bulbs, will cease producing incandescent bulbs in 10 years. Australia has mandated the use of energy-efficient lighting and already banned the importation of “non-compliant lighting,” which translates into a minimum energy standard for a light source of 15 lumens/W. Several other countries are planning to ban and phase out incandescent light bulbs, including Italy, Canada, the United Kingdom, Switzerland, and the Philippines.
HIGHER-EFFICIENCY PRODUCTS More LED lighting products that meet industry and government standards for lifetime and output lumen depreciation levels are emerging. One such standard is the L70 Energy Star lifetime requirement, which means 70% lumen depreciation in an LED from the initial lumen output. Presently, the industry uses a figure of about 50,000 hours of operation before lumen depreciation sets in.
In collaboration with Samsung Electro-Mechanics, researchers at Rensselaer Polytechnic Institute developed and demonstrated a polarization-matched device that exhibits an 18% increase in light output and a 22% increase in ac wall-plug efficiency (Fig. 2). This new device notably reduces the “efficiency droop” that affects LEDs (largely due to electron leakage).
Cree, a major manufacturer of high-brightness LEDs, offers the most devices that meet stringent U.S. Department of Energy (DoE) Energy Star performance criteria for use in fixtures or luminaires. The DoE has accepted Cree’s LM-80 test data for the company’s XLamp XR-E, XP-E, and MCD LEDs, allowing such products to be submitted to fixture manufacturers (Fig. 3). The Illumination Engineering Society of North America (IESNA) adopted the LM-80 standard as an “Approved Method for Measuring Lumen Maintenance of LED Light Sources.”
Marc McClear, director of Cree’s business development for solid-state lighting, says we shouldn’t expect to see much direct replacement of incandescent or fluorescent bulbs with LEDs in the same socket, at least not in the short term. It’s simply not practical to place a modern high-brightness LED into the same socket, since it dissipates a lot more heat than the bulb it’s replacing.
Instead, McClear sees more of a growth market in replacing light bulbs in existing can and overhead fixtures at the junction box in the ceiling, emphasizing that designers should think in terms of fixtures and heat and photon management, as well as light sources. He also foresees a large market for using highbrightness LEDs in outdoor facilities, street lighting, and architectural lighting.
“Two years ago, it simply would not have been practical to use LEDs for street lighting,” McClear says (see “High-Brightness White LEDs Light The Way To Greener Illumination”). “A year ago, the idea was barely into the trial stage. A few cities would replace the fixtures on one block of one street. This year, it’s full steam ahead around the world.”
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