Digital Displays Explained

What About Those Other Terms?

You’ll encounter a lot of other confusing acronyms, initialisms, and terms when reading about digital displays. There are too many technical terms and marketing buzzwords to list them all, but here’s a brief description of some of the more common ones.

LED: The light behind an LCD panel is one of two major varieties. The first type is CCFL (cold cathode flourescent lamp), a technology that's sort of like the fluorescent bulbs in your home, only thin and flat. The other type is LED (light-emitting diode). Using LEDs typically gives a TV a wider color range, a longer life, and lower power consumption. Some TVs have LEDs only along the edge (marketed as “edge-lit LED”), which is less desirable because it makes achieving high brightness and even lighting difficult.

TFT: A thin-film transistor is a thin substrate, like glass, coated with various thin films of metal, silicon, or plastic. The idea is to form a big sheet of very small switching transistors and capacitors. It’s simply a means of changing the current applied to individual pixels on a display--virtually all active-matrix displays, from AMOLED displays to nearly all LCDs, use TFTs.

Active matrix: This is a system for individually controlling each subpixel with a series of transistors and capacitors (see: TFT). It allows for more precise voltage control and faster switching than passive-matrix technology does. Nearly all digital displays today are active matrix.

Passive matrix: This technology controls the voltage of individual subpixels with a simple grid of conductive materials. Almost no LCD uses this form of addressing subpixels anymore, since the price of TFTs has dropped and the quality has improved. Passive-matrix technology generally produces less precise control over color and pixel response than active-matrix technology does.

An arrangement of standard red, green, and blue subpixels.
An arrangement of standard red, green, and blue subpixels.
Subpixel: On all digital displays, a single pixel (one picture element meant to be able to represent any color) is actually formed of several smaller subpixels. Typically each pixel consists of red, green, and blue subpixels; the display alters the brightness of these three colored subpixels to produce any color or shade. Because the subpixels are too small to see individually, our eyes see the combination of the three subpixels as one blended color. Some displays have a fourth subpixel color (usually white or yellow), but that isn't very common.

The PenTile arrangement of subpixels on the Google Nexus One's AMOLED screen.
The PenTile arrangement of subpixels on the Google Nexus One's AMOLED screen.
PenTile: The red, green, and blue subpixels that form a single pixel on a digital display are usually long, evenly sized rectangular stripes. In PenTile displays, the subpixels are not identical, but instead have different sizes and shapes. The PenTile arrangement works in conjunction with a specially designed display controller that takes the irregular number and size of these subpixels into account. The goal is to produce a greater number of effective pixels with fewer subpixels.

Defining the resolution of a PenTile display has been the subject of some controversy, as the technology relies on using some subpixels in two neighboring pixels. The Google Nexus One smartphone prominently featured an AMOLED display with a PenTile subpixel arrangement. PenTile is a trademark of Samsung.

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