Liquid-crystal displays (LCDs) are everywhere, from cell phones and cameras to laptops and flat-screen TVs, but they’re still relatively inefficient and limited in color quality. At best, only about 7 percent of the backlight illumination makes it through roughly 20 layers of optics, electronics, and filters to reach a viewer’s eyes. And these filters ensure that the resulting colors are dull compared to some other displays, for example those made with organic light-emitting diodes (LED).
QD Vision, a startup based in Cambridge, MA, has developed a technology that it claims will improve the efficiency of LCDs by 40 percent. In addition, the company says it will provide purer colors, allowing the displays to produce high-dynamic range, which features better contrast between the darkest blacks and the whitest whites.
The technology, called a quantum light optic, will be sold to three of the five major LCD manufacturers and integrated into commercial displays by 2011, says Seth Coe Sullivan, founder and chief technology officer of QD Vision.
Quantum dots are at the heart of the quantum light optic technology. These dots are nanoscale crystals of semiconductors that emit pure colored light. When quantum dots are added to existing lighting technology, such as the light-emitting diodes found in LCD backlights or those found in light bulbs, they shine so brightly that they reduce the number of diodes needed to achieve the same overall brightness. Furthermore, since quantum dots shine at specific colors, they can be added to a white LED to improve the spectral properties of its light.
QD Vision, which was spun out of research at MIT, is already using quantum light optic technology to improve the efficiency of light-emitting diodes. The first lighting products based on the technology will be available by February 2010, says Sullivan.
Quantum dots can also improve efficiency and color purity of displays. While some larger LCDs are illuminated using cold-cathode fluorescent lights, most small displays are lit up with white LEDs. Manufacturers attach a strip of white LEDs to the edge of a plane of glass. This glass spreads out the light and, because of special texturing on its surface, it directs the light out toward a viewer.
The type of white LED that manufacturers use for the backlight consists of a mixture of semiconducting materials that produce blue light and a phosphor that produces yellow. Energy from the blue light causes the phosphor to glow, producing a yellowish white light. To produce multiple colors, for the red and green subpixels used in a display, manufacturers add color filters. These filters separate out red and green light from the white LED.