Light-emitting diodes (LEDs) have been used as indicator lights and displays for many years. However, because of their low levels of light output and the lack of color options, LEDs were limited to these few applications. Recent advances in technology, materials and production processes are now opening the way for LEDs to be used in a vast array of lighting applications.

According to Andrew Bierman, M.S., lighting systems specialist and adjunct assistant professor of architecture at Rensselaer Polytechnic Institute, Troy, N.Y., LEDs are solid-state semiconductor devices that convert electrical energy directly into light.

“An LED is a semiconducting chip which is made of various chemicals and gases. When current passes through the chip, photons are created and light is emitted,” explained Doug Silkwood, director of communications for LumiLeds Lighting, LLC, San Jose, Calif. It is the chemistry of the chip that determines the light color.

LEDs have been around for more than 30 years. At first, only red LEDs were used. The two most significant advances in the 1990s were the development of both high-brightness and blue LEDs. “The development of the blue LED led to the ability to mix blue, red and green light to create white LEDs,” said Dr. Chips Chipalkatti, director of North America LED modules for Osram Sylvania Products, Inc., Danvers, Mass.

The ability to create white light with LEDs potentially opens up a wide range of general lighting applications for this technology. Brighter light output also makes it more attractive. “In 1970, one LED chip produced 1/100th of a lumen. Today, one chip can produce 25 lumens,” Chipalkatti said.

Unlike incandescent lamps, LEDs are more energy efficient because they produce light in a single wavelength. “Since a narrow band of light is produced, there’s less waste,” according to Bill Ryan, group product manager for LEDs at Philips Lighting Co., Somerset, N.J.

“LEDs are more energy efficient because electricity is being directly converted to light without generating much heat,” added Chipalkatti.

Industry research and development is constantly underway to create different chemical variations in the chips to produce even further efficiencies. “Right now, white LEDs are producing 20 to 25 lumens per watt and color LEDs can get as high as 60 lumens per watt, while incandescent bulbs produce only 15 lumens,” said Silkwood.

Other benefits of LEDs include longer life (up to 100,000 hours of use) and reduced maintenance costs, better-quality light output with minimum ultraviolet and infrared radiation, durability, programmability and smaller flexible light fixtures.

LED applications

LEDs make up an estimated 80 percent of the exit sign market, according to a survey conducted by RPI’s Lighting Research Center of exit sign representatives in 1998. Other popular applications include automotive signal and interior lighting, large-screen television displays, outdoor residential photovoltaic lighting and backlighting applications. “Signage is one of the fastest-growing applications for LEDs,” said Chipalkatti. He also predicted that LEDs will soon gain market share in architectural, spotlighting and accent lighting. Ryan added pathway applications to the list, or any other area that color rendition is not critical. “The next step is to increase the output of white LEDs.” Ryan estimated that such white LED products will be coming to market in the next three years.

Next step

A major challenge facing the LED industry is to develop new ways to extract light from the chip, further reducing any energy wasted through heat generation. More important, to improve their competitiveness, LEDs will have to increase their light output while reducing the number of chips needed to produce the light source. Such improvements have already been made; in the late 1980s, there were 250 to 300 LED chips in a single traffic light and in the late 1990s, that number was reduced to between 12 and 18 chips.

Cost reduction is another goal for the LED industry. “LEDs are still more expensive than traditional lighting methods on an up-front capital expenditure basis,” said Silkwood. In the long run, however, LEDs are more cost effective for many applications because of their long life and reduced maintenance requirements and costs and energy costs.

According to Ryan, the major issues facing the LED industry are increased light output, reduced costs and improved white color. “Only when white LEDs can produce enough light at a reasonable cost for general lighting applications will they be accepted as a replacement for incandescent and fluorescent lighting,” he said. The National Energy Bill being considered by Congress calls for $.5 billion in funding to research and improve white LEDs. EC

BREMER, a freelance writer based in Solomons, Md., contributes frequently to ELECTRICAL CONTRACTOR. She can be reached at 410.394.6966 or by e-mail at dbremer@erols.com.