A light with a bright future
Light bulbs have blazed for more than 125 years, and people still can't seem to get enough of them. Priced at less than a dollar apiece, and screwed into billions of sockets worldwide, these glowing little orbs have changed the way humanity works and plays, turning night into day. But as energy costs soar, the future of the traditional incandescent light bulb is beginning to dim.
Futuristic solid-state lighting has already crept into consumer goods, such as cellphone screens and desk lamps. Light-emitting diodes (LEDs) and their cousins, organic light-emitting diodes (OLEDs), are two developing light sources beginning to beam into homes and offices. LEDs are showing up in night lights, flashlights, outdoor pathway lights, and Christmas lights. OLEDs are not as prevalent, but cellphones, notebook computers, and TVs made with them are moving from prototypes into products.
Those involved in lighting research say these new technologies will revolutionize the way we use lighting over the next decade. Because they can be made into extremely thin, flexible glowing sheets, designers envision:
• Ultralight, wall-size TVs.
• Electronic newspapers that can be rolled up and constantly updated.
• Under-cabinet surfaces that glow to light up kitchen counters.
• Clothes with electronic displays woven into them.
• Windshields that display information for the driver.
• "Smart windows" that double as TVs or computer screens, or that let in light during the day and glow at night.
• Easily movable light-emitting panels or light walls for homes or offices. The white light could be turned to "cooler" or "warmer" shades of color as desired.
• "Smart" goggles or helmets with displays for soldiers, police, or scuba divers.
LEDs, an older technology, are about five to eight years ahead of OLEDs - which, unlike LEDs, use organic polymers, such as proteins and DNA, to create light, says Nadarajah Narendran, research director at the Lighting Research Center (LRC), Rensselaer Polytechnic Institute in Troy, N.Y.
"Some high-end homes are already using LED [lights] to improve aesthetics," he says. And OLEDs should rise from about 60 million units produced in 2005 to about 280 million in 2010, according to a forecast by semiconductor industry tracker iSuppli in El Segundo, Calif.
Both LEDs and OLEDs need to drastically lower their cost and increase their energy efficiency before they can threaten the light bulb. "Flat-panel displays [computer and TV screens] sell for a lot more than light bulbs," says Bill Feehery, business director of DuPont OLED Displays. That's why the new lighting technologies will be seen there first, he says. [Editor's note: The original version misidentified Mr. Feehery's title.]
Today's incandescent light bulb really should be called a heat lamp, since it gives off most of its energy as warmth. Incandescent bulbs emit 10 to 15 lumens of light per watt consumed. Fluorescent tubes are much more efficient, giving off 60 to 80 lumens per watt. OLEDs now produce 20 to 30 lumens per watt. The US Department of Energy has challenged the industry to produce OLEDs with 100 lumens per watt by early next decade.
"The big-picture goal [for OLEDs] is to get to lighting," says Janice Mahon of Universal Display Corp., a leading OLED developer in Ewing, N.J. "We're not there yet." She envisions OLED lighting that "you could roll onto your ceiling like wallpaper" or wrap around poles.
Besides their potential efficiency, OLEDs will be easier to recycle because they are lightweight. Materials used in them are more benign than those found in current lighting fixtures, which often contain hazardous materials such as mercury.
While LEDs already have long life spans, developing white-light OLEDs or WOLEDs, which combine red, green, and blue light to form white light, has been a challenge. The phosphorescent blue dyes tend to burn out quickly.
But that problem may be solved. A group of scientists say they've found a way to use a fluorescent dye for the blue element, prolonging its life span and increasing the energy efficiency of OLEDs by 20 percent. The group, headed by Mark Thompson at the University of Southern California and Stephen Forrest at the University of Michigan, reported their findings last month in the journal Nature. Their research, funded by Universal Display, is one of many breakthroughs in the field, Ms. Mahon says.
In March, German researchers at the Technical University of Braunschweig said they created the first truly transparent OLED, which is clear when turned off and can emit colored or white light when activated. That's led to speculation that transparent video screens, such as the one used by Tom Cruise in "Minority Report," are closer to science fact than science fiction.
Meanwhile LEDs, invented in 1962, are coming into wider use in their own right. Sony and Toshiba laptop screens use them. Samsung has shown a 45-inch TV with LED backlighting, says Kim Allen, director of display technology and strategy at iSuppli. But LEDs must also bring costs down, and they face a special problem with heat management. A great deal of heat is generated at their base, Ms. Allen says. Putting an LED into a conventional "Edison socket," she says, would melt it. LEDs used in cellphones or other flat-panel technologies can dissipate heat better.
LEDs and OLEDs may overlap in some uses, but each is likely to find its own niche, experts say. LEDs pump out lots of bright light and excel when used in flashlights and desk lamps. OLED light is more diffuse and suitable for display screens.
TV manufacturers seem eager to get OLEDs into their products. "One of the Holy Grails ... has been to come up with something that can perform as well as or better than an LCD [liquid crystal display] but can be manufactured more easily and at a lower cost," Mr. Feehery says.
In comparison with today's liquid crystal display (LCD) screens, for example, OLED screens have a wider array of colors and blacker blacks. They display quick movements with less blurring and provide wider viewing angles.
While OLEDs may conquer video screens - beginning with cellphones and working their way up to home entertainment systems - they won't vanquish the lowly light bulb for a while.
The general view is that OLED lights won't start taking market share from light bulbs for five to 10 years. But with the pace of technological advances quickening, that estimate may be too conservative. "It can happen pretty quickly," Mahon says.
