New LCD technologies advance the state of the art
To get high performance, LCD (now including 3-D) display manufacturers use IPS (In-Plane Switching), which improves the viewing angle and color performance of the LCD panels. With this technology, the crystal molecules change the luminance at each pixel by twisting parallel to the plane of the panel instead of perpendicular to it, reducing light scattering and therefore increasing contrast, as well as viewing angle.
In a conventional TN-TFT (Twisted-Nematic Thin-Film Transistor) LCD display, when a pixel transistor is activated, the crystal compounds untwist, changing the angle of polarization of the transmitted light. The main drawback of TN technology is that the alignment of the crystals varies the farther away they are from the transistor electrode, turning at right angles to the substrates. This impairs the transmission of light, causing a drop in contrast, brightness and color saturation at wider angles to the screen.
IPS improves viewing angles of TFT monitors considerably but requires two transistors at every pixel instead of the one needed for a TN-TFT display. This means that more of the transparent area of the display is blocked from light transmission, so a brighter backlight is required. One other benefit of an IPS panel is that the pixels pass light when in the active state and block it in their passive state (when no voltage is applied), so if a pixel transistor fails, the corresponding pixel will always remain black, unlike those in a TN-TFT panel, which can get stuck “on.”
A 10-bit IPS LCD panel, coupled with an RGB-LED backlight, can provide an exceptionally wide color gamut, even expanding the ITU-R BT.709 standard by 30 percent, enabling it to display a greater range of colors than conventional LCD and CRT displays. IPS technology can also provide superior performance with high contrast (1000:1 contrast ratio or more) and brightness.
Panel developments continue
OLED (Organic Light Emitting Diode) displays offer advantages over LCDs as well: high contrast ratio, deeper blacks, faster refresh rates, wider angles of view, lower power consumption and wider color gamut. Because OLED doesn’t require backlighting, the overall thickness of the screen can also be greatly reduced. All this comes at a price premium, and there are questions about the lifespan of OLED displays. But several manufacturers are actively developing the technology, and — as is historically the case — the consumer market will continue to drive the evolution of video displays.
—Aldo Cugnini is a consultant in the digital television industry and a partner in a mobile services company.