However, the phosphor light produced by most LEDs is made up of a smear of different colors, says Sullivan. “There’s a little red light in the yellow phosphor, and there’s a little bit of green light in the yellow phosphor,” he says. To let enough brightness through, color filters need to be spectrally broad, but this means they also let through a mixture of color, which hurts its quality.
When a quantum light optic is placed over a blue LED, it eliminates the need for the yellow phosphor altogether. The light from the blue LED excites electrons in the quantum dots and–depending on the size of the dots used–a specific color of light is produced. A cadmium selenide dot that’s six nanometers wide, for example, produces red light; a dot that’s four nanometers wide produces green light; and one that’s two nanometers wide produces blue light. So instead of a yellowish white light, the light consists of purer red, blue, and green.
With quantum dots, manufacturers can use LCD color filters that only let pure colors of light through. Sullivan claims that quantum dots can improve an LCD’s color gamut, or color range, by 80 to 100 percent.
Additionally, fewer LEDs are needed to achieve the same result. And the LEDs that are needed are simpler and cheaper than those with the yellow phosphor. “All of a sudden,” says Sullivan, “your TV is as good as your CRT [cathode-ray tube] was 10 years ago in terms of color, and there’s also a manufacturing cost savings to LCD makers, which is a big deal.”
Manufacturers are increasingly looking to use LEDs in the backlights of larger displays. The California Energy Commission recently announced that it is imposing new power consumption limits on high-definition television sets in the state, the biggest market for such sets in the U.S., by 2013. Since LEDs are more energy efficient than cold-cathode fluorescent lights, quantum dots could “be a good way to make LED backlights better, more efficient, and more cost-effective,” says Bruce Berkoff, chairman of the LCD TV Association.”
Hear more from MIT at EmTech MIT.