Quantum Leap in Lighting
QD Vision is using its quantum dots in LED lighting to produce more pleasing white light.
Seth Coe-Sullivan flicks the switches on two desk lamps, and even from across the conference room, it’s immediately obvious which light the chief technology officer of QD Vision is there to brag about. The light coming from the lamp on the left is a harsh bluish white. The lamp on the right casts a warmer, more yellow glow. Coe-Sullivan holds a hand under each lamp. The hand under the bluish light looks pale and sickly; the other looks darker and healthier. The harsher light lacks wavelengths in the red end of the spectrum, so there’s no light to illuminate the reddish tinge that blood provides to human skin.
QD Vision, based in Watertown, MA, is promoting a new LED-based lamp that it made with Nexxus Lighting of Charlotte, NC. Nexxus makes a lamp designed to screw into standard sockets used in recessed ceiling lighting. It consists of an array of white-light LEDs encircled by fins that remove excess heat. QD Vision adds an optic–a plastic cover with a special coating that snaps into place over the LEDs.
It’s that coating that makes the difference in the quality of the light. It consists of quantum dots–tiny bits of semiconductor material just a few nanometers in diameter. When excited by a light source–in this case, the LEDs–quantum dots radiate light in a wavelength that varies according to the size of the dot: a two-nanometer dot gives off blue light, a four-nanometer dot emits green, and a six-nanometer dot produces red. The company makes the dots in controlled sizes, then mixes them in the right ratio to get the desired color.
This color-tailoring ability solves one of the major problems with using LEDs for general lighting applications. LEDs are appealing because they last for years, use perhaps 20 percent of the electricity of a standard incandescent bulb, and are highly efficient at converting electricity into visible light instead of into heat. But to make white light, you either have to mix together LEDs of different colors or use a blue LED coated with a phosphor that emits yellow light to produce a whitish mix. The problem with the phosphors is that they don’t emit evenly across the visible spectrum. They tend to have gaps in the green section and even more so in the red, leading to the harsher, bluish light. “You can’t precisely tailor phosphors anywhere in the visible spectrum,” says Dan Button, QD Vision’s CEO.
The QD Vision optics absorb the energy from the phosphor-coated LEDs and reemit it at a new mix of wavelengths. Coe-Sullivan says that the color rendering index–a measure of what colors look like under the light–of the company’s optic is 90, compared with the 70s for the LEDs without the optic. Sunlight has a color rendering index of 100, and standard incandescent lightbulbs about 99. The QD Vision light is far more efficient than an incandescent, producing 65 lumens per watt of electricity, whereas an incandescent produces about 15 lumens per watt. A compact fluorescent lightbulb produces about 30 lumens per watt; has a cooler, harsher light than the QD Vision lamp; and has the added environmental problem of containing mercury.
“These are good numbers,” says Nadarajah Narendran, director of the Lighting Research Center at Rensselaer Polytechnic Institute. “This may be the first market-ready product [based on quantum dots], so in that sense they might be unique,” he says. “You have to have all the ingredients right.” Those include not only lifetime, energy efficiency, and color: “Price is the most important one at the moment.”
Companies are struggling to get the cost of their LED-based bulb replacements down to $65 and below. The Nexxus lamp could cost about $100. Button says that if you consider how much a user will save in electricity, the cost of replacement bulbs, and the labor that would otherwise be needed to replace multiple ceiling fixtures over the projected seven-and-a-half-year lifetime, the lamp will be competitive.
The two companies displayed their lamp last week at the Lightfair International trade show in New York, and they say that they’ll have it available for sale by the end of the year. Meanwhile, Button says that there’s nothing exclusive about QD Vision’s deal with Nexxus, and that he hopes to work with other companies to produce more products for general lighting. QD Vision had initially focused on using quantum dots to make better display screens for computers and other devices. It’s still in that business, but given that most of the display makers are in Asia, the company felt as though lighting would give the company a quicker entry into the market, Coe-Sullivan says.
The beauty of QD Vision’s technology, Button says, is that it’s just a small addition to existing LEDs designed for standard light fixtures. “They’re getting a market without changing anything,” he says. “You give us a light input, and we’re going to improve the color without diminishing the efficiency.”