Flat Panel Display | Emissive and Non-Emissive in Computer Graphics


Flat Panel Display | Emissive and Non-Emissive

Flat Panel Display | Emissive and Non-Emissive

As CRT and DVST have large volume, and weight and require large power consumption they are outdated devices and are replaced by Flat Panel Derives.

Types of Flat Panel Display Devices

Flat Panel Display

·        Emissive Display Devices

o   Plasma Panel Devices

·        Non-Emissive Devices Display

o   Liquid Crystal Display

Emissive Display Devices

These devices work by converting electric energy into light. The various devices are plasma panels, light-emitting diodes. A major example of a flat panel display is the plasma panel display.

Plasma Panel Display

It is a device in which each pixel remains bright after it has been intensified. It is very similar to DVST though its construction is very difficult. Plasma pan display writes images on the display surface point by point, each point remains bright after it has been intensified. This makes the plasma panel functionally very similar to the DVST even though its construction is markedly different.

construction of plasma panel display.

Figure 1.9 shows the construction of the plasma panel display. It consists of two plates of glass with thin, closely spaced gold electrodes. The gold electrodes are attached to the inner faces and covered with a dielectric material. These are attached as a series of vertical conducting ribbons on one glass plate, and a set of horizontal ribbons to the other glass plate.

The space between two glass plates is filled with neon-based gas and sealed. By applying voltages between the electrodes the gas within the panel is made to behave as if it were divided into tiny cells, each one independent of its neighbors. These independent cells are made to glow by placing a firing voltage of about 120 volts across it by means of the electrodes. The glow can be sustained by maintaining a high-frequency alternating voltage of about 90 volts across the cell. Due to this refreshing is not required.

Construction of Plasma Panel Display

The plasma panel display consists of two thin glass sheets with gold electrodes arranged horizontal and vertical on the corresponding glass sheets. The region between the glass plates is filled with a Neon gas.

By applying voltage the gas within the cell breaks down into electrons and ions and the glow starts. Once the glow starts, the voltage can be decreased up to which glow continues.

Advantages of Plasma Panel Display

1) It produces a steady image, totally free of flickers.

2) Requires small space.

3) Requires low voltage and power supply.

Disadvantages of Plasma Panel Display

1) It has low resolution

2) It is very costly. 

Non-Emissive Display Devices 

These devices work by using optical effects to convert sunlight or light from some other source into graphics patterns. Liquid crystal is the most common example of a non-emissive flat panel display device. A major example of a flat panel display is the liquid crystal display.

Liquid Crystal Display (LCD)

It is a non-emissive device that produces a picture by passing polarized light through a liquid–crystal material that can be aligned to either block or transmit the light. LCD is given a name so, because the compound filled between the glass plates is a crystalline arrangement of molecules, hence they flow like a liquid.

Construction of Liquid Crystal Display

It consists of two glass plates, each containing a light polarizer at right angles to the other plates, with threadlike liquid crystal filled in between. The Molecules of Nematic are arranged such that polarized light passing through the material is twisted so that it will pass through the opposites polarized. The light is then reflected back to the viewer. To turn off the pixel, one applies voltage to the interacting conductors to align the molecules so that the light is not twisted. The different layers of LCD are shown in figure 1.10.

different layers of LCD

Advantages of LCD

1) Very compact and light.

2) Low power consumption.

3) No geometric distortion.

4) Little or no flicker depending on backlight technology.

5) Not affected by screen burn-in.

6) Can be made in almost any size or shape.

7) No theoretical resolution limit.

Disadvantages of LCD

1) Limited viewing angle, causing color, saturation, contrast, and brightness to vary, even within the intended viewing angle, by variations in posture.

2) Bleeding and uneven backlighting in some monitors, causing brightness distortion, especially toward the edges.

3) Smearing and ghosting artifacts caused by slow response times (>8ms) and “sample and hold” operation.

4) Only one native resolution. Displaying resolutions either requires a video scaler, lowering perceptual quality, or display at 1:1 pixel mapping, in which images will be physically too large or would not fill the whole screen.

5) Low bit depth results in images with unnatural or excessive contrast.

6) Dead or stuck pixels may occur during the manufacturing or through use.

7) Not all LCDs are designed to allow easy replacement of the backlight.

8) Cannot be used with light guns/pens.

9) Loss of contrast in high-temperature environments.