PDP splicing, DLP splicing, and LCD Splicing

2018-12-17

I. Comparison of Imaging Principles

a) Plasma Principle

PDP (Plasma Display Panel), also known as plasma display, is a type of display technology that uses gas discharge. Its working principle is very similar to that of fluorescent lamps. It employs plasma tubes as the light-emitting elements, with each plasma tube corresponding to a pixel on the screen. The screen is based on glass, spaced at certain distances, and sealed hermetically around the edges to form individual discharge spaces. These spaces are filled with a mixture of inert gases such as neon and xenon as the working medium. Metal oxide conductive films coated on the inner surfaces of the two glass substrates serve as excitation electrodes. When voltage is applied to the electrodes, the mixed gas in the discharge space undergoes plasma discharge, also known as the plasma effect. Gas plasma discharge produces ultraviolet light, which excites the phosphor screen coated with red, green, and blue phosphors, causing it to emit visible light and display images. By achieving 256 levels of grayscale for each color component and then mixing colors, full-color display is realized.
The technical principle is that since the plasma tubes that emit light in a PDP are evenly distributed in the plane, the center and edges of the displayed image are completely consistent, eliminating distortion and achieving true flatness without any image distortion. Since there is no electron beam movement during the display process and no need for electromagnetic fields, external electromagnetic fields do not interfere with it, making it highly adaptable to environmental conditions. PDP is an autoluminescent display technology that does not require a background light source, thus avoiding issues with viewing angle and brightness uniformity. The design where the three primary colors share the same plasma tube also eliminates focusing and convergence problems, allowing for very clear images.
Plasma displays have high operating voltages and consume a lot of power, resulting in large energy consumption. They have inherent limitations in lifespan; after using them for 5,000 to 10,000 hours, the screen brightness will decrease by half, and they may not function properly above an altitude of 2,500 meters.

b) DLP Principle

DLP stands for "Digital Light Processing." It refers to a technology that first processes image signals digitally before projecting light. This process is based on the digital micromirror device (DMD) developed by Texas Instruments, which is the final step in displaying digital visual information. The DMD stands for Digital Micromirror Device, literally meaning a digital micromirror element. This refers to the core component of the optical engine heart in DLP technology systems—the digital micromirror chip. It is formed by adding a rotating mechanism that can adjust the reflective surface onto the standard CMOS semiconductor process. To be more specific, DLP projection technology uses a digital micromirror chip (DMD) as the main key component to achieve the digital optical processing process. Its principle involves using an integrator to evenly distribute light from a source, then splitting the light into red (R), green (G), and blue (B) colors through a color wheel, imaging the colors onto the DMD. The digital signals from the rotating mirror are synchronized to convert continuous light into grayscale, and with the combination of R, G, and B colors, the desired colors are displayed before being projected through a lens. From the technical principles of DLP, it has the following advantages:

1 Noise Advantage: The inherent digital nature of DLP allows for the elimination of noise because DLP has the capability to complete the last link in the digital video infrastructure, and it provides a platform for developing a digital visual communication environment. DLP technology offers a projection method that can achieve the display of digital signals, thus completing the full digital infrastructure with minimal signal noise.

2 Exact grayscale levels: Its digital nature allows for precise image quality with exact digital grayscale levels and color reproduction.

3 Reflection Advantage: Since the DMD is a reflective device, it has an optical efficiency of over 60%, making the DLP system display more efficient. This efficiency is the result of reflection rate, fill factor, diffraction efficiency, and the actual 'on' time of the lens.

4 Seamless Image Advantage: 90% of the pixel/lens area can effectively reflect light to form a projected image. The entire array maintains uniformity in pixel size and spacing, and is not dependent on resolution. The higher the DMD fill factor, the higher the visible resolution, thus creating more realistic and natural lifelike projection images than those from conventional projectors with line-by-line scanning.

5 Reliability: The DMD has passed all standard semiconductor qualification tests. It has also passed barrier tests simulating the actual operational environment conditions of the DMD, including thermal shock, temperature cycling, humidity resistance, mechanical shock, vibration, and acceleration tests. Based on thousands of hours of life and environmental testing, DMD and DLP systems exhibit inherent reliability. The advantages and disadvantages brought by the display principle are revealed.

c) Liquid Crystal Display

The LCD (Liquid Crystal Display) is the abbreviation for Liquid Crystal Display. The structure of an LCD involves placing a liquid crystal between two parallel glass plates. Within these glasses are numerous vertical and horizontal thin wires that control the direction of rod-like crystal molecules by turning them on or off, thereby refracting light to produce images. An LCD consists of two glass panels, each about 1mm thick, separated by a uniform gap containing liquid crystal material of 5μm. Since the liquid crystal material itself does not emit light, there are lamp tubes on both sides of the display as light sources. Behind the LCD panel is a backlight plate (also known as a diffuser plate) and a reflective film. The backlight plate is composed of fluorescent substances that can emit light, and its main function is to provide a uniform background light source.

The light emitted by the backlight panel enters the liquid crystal layer, which contains thousands of liquid crystal droplets. The droplets in the liquid crystal layer are all contained within a fine cell structure, with one or more cells making up a pixel on the screen. Between the glass plate and the liquid crystal material are transparent electrodes, which are divided into rows and columns. At the intersections of these rows and columns, the optical rotation state of the liquid crystal is changed by varying the voltage, acting like small light valves. Around the edges of the liquid crystal material are the control circuit section and the drive circuit section. When an electric field is generated by the electrodes in the LCD, the liquid crystal molecules twist, thereby refracting the passing light in a regular manner. This light then passes through the second layer of filter to be displayed on the screen.

LCD splicing (Liquid Crystal Display Splicing) is a new splicing technology that has emerged in recent years, following DLP and PDP splicings. LCD splicing walls have advantages such as low power consumption, light weight, long lifespan (generally 50,000 hours of normal operation), no radiation, and uniform picture brightness. However, their biggest drawback is that they cannot achieve seamless splicing, which is somewhat regrettable for industry users who require very precise display images. Since liquid crystal panels have a frame at the factory, splicing them together will result in a frame (gap). For example, the frame of a single 21-inch LCD panel is generally 6-10mm, and the gap between two spliced panels can be as large as 12-20mm. To reduce the gaps in LCD splicing, there are several methods currently used in the industry. One is narrow-gap splicing, and another is micro-gap splicing. Micro-gap splicing involves removing the outer shell of the purchased LCD panels and splicing the glass to glass, but this method carries a higher risk. If the LCD panels are not disassembled properly, it can damage the quality of the entire panel. Currently, only a very few domestic manufacturers use this method. Additionally, after 2005, Samsung introduced a dedicated splicing LCD panel—DID (Digital Information Display) panels. DID panels are designed specifically for splicing and have their frames made very small at the factory.

The three major technical features of PDP plasma, DLP and LCD liquid crystal are:

DLP splicing advantages:

DLP splicing disadvantages:

Advantages of PDP splicing:

Advantages of LCD Liquid Crystal Pano:

II. Comparison of Application in Partition Walls

For splicing applications, both methods have their own advantages and disadvantages:

Full Screen Control:

LCD: An interactive control system that can open multiple windows, each displaying different images.
PDP: Due to the small display area per screen and the need for more screens of the same size, the controller costs are higher, the speed is slower, and it cannot flexibly open windows to display images.
DLP: Controls with high speed and functionality, not limited by physical screens for display, can arbitrarily open windows to display images in space and installation.
LCD: Ultra-thin body, easy and quick installation, occupies less space, and is thinner and lighter than PDP.
PDP: Ultra-thin body, easy and quick installation, occupies less space.
DLP: Requires a larger installation space and maintenance space for screen uniformity.
LCD: The color uniformity and brightness uniformity between each screen can be very good.
PDP: The color uniformity and brightness uniformity between each screen are not easy to adjust, resulting in poor overall screen consistency.
DLP: Uses digital technology, making it easy to adjust brightness and colors, with fewer screens resulting in high overall screen uniformity, suitable for display environments.
LCD: Suitable for installation in conference rooms, monitoring rooms, large shopping malls, and shopping centers, can display static or dynamic video signals, 7*24 hours on-duty, running all year round.
PDP: Suitable for installation in conference rooms, with a display area of less than 6 square meters, and mainly displaying dynamic video signals, used for occasions where the annual running time is less than 1000 hours.
DLP: Suitable for controlling or larger display spaces and areas, suitable for displaying various signals, installed in environments with longer annual running times.
LCD: Low power consumption, low installation environment requirements.
PDP: Extremely high power consumption, large heat dissipation, requiring high installation environment requirements for electricity and air conditioning.
DLP: Low power consumption, low installation environment requirements for maintenance.
LCD: Low maintenance cost, supports 7*24 hours uninterrupted operation, with a service life of over 50,000 hours.
PDP: High maintenance cost, if the brightness decays to very low levels, it is necessary to replace the display board to increase brightness, which costs the equivalent of buying a new one.
DLP: High maintenance cost, when the brightness is insufficient, it is necessary to frequently replace bulbs to increase brightness, resulting in increasing costs. Conclusion

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