CRT and LCD are well-known display technologies that have undergone significant developments in recent years. LCD in particular has seen noteworthy adoption, however, there are a new breed of technologies that are set to level the playing field.
Andr'e Rossouw, Toshiba product manager at Rectron, takes a closer look at the development of LCD and gives readers glimpse into the future of display technologies.
When notebooks were introduced in the late 1980`s, most of then came with monochrome, passive-matrix LCD (liquid crystal display) screens.
Although these displays met many of the requirements that are still important today, most mobile users were happy to switch to an external CRT (cathode ray tube) when working in the office.
CRTs offered higher resolution, supported colour and presented its users with much wider viewing angles - in fact, for optimal viewing LCD users had to sit directly in front of their monitors.
Moreover, early LCDs were subject to effects such as "ghosting" (as the cursor moves across the screen it leaves a trail of images scattered behind it) or "submaring" (the cursor-image disappears entirely as it moves across the screen).
It was not until active matrix displays emerged that LCD technology really matured.
Today, due to continuous advances in LCD technologies, the gap is closing. Many 17-inch LCDs today compete favourable with 19-inch CRTs.
Understanding LCD
The first prototype LCD, introduced by the Radio Corporation of Americe (RCA) in the 1960s, was made of twisted nematic (TN) liquid crystal.
Since then, enhancements such as super twisted nematics (STN), dual scan twisted nematics (DSTN), ferroelectric liquid crystal (FLC) and surface stabilised ferroelectric liquid crystal (SSFLC) have been introduced.
Liquid crystals are naturally twisted, but applying an electric field untwists them to varying degrees, depending on the voltage. When they are straightened out, liquid crystals change the angle of the light passing through them.
Therefore, by selectively supplying voltage, the LCD harnesses the potential to block or display light in order to create the desired image on the screen. To produce an image, glass embedded with a grid of electrodes sandwiches the liquid crystals, allowing the individual pixels to be turned on or off.
For a colour display, the pixel is then further separated into three, using a red, green or blue filter - these colours are mixed in varying intensity to produce a full palette of colours on the screen.
Throughout the development of LCDs, the real enhancements and performance advantages have been by made by changing the grid or matrix controls, the angle and flow of light, as well as liquid crystal improvements.
Today`s and tomorrow`s technologies
There are a number of technologies that are gaining momentum, paving the way for even thinner and lighter designs.
Ultra-high-resolution displays - polysilicon TFT LCDs
Polysilicon LCD is a technology that is particularly suited for the miniaturisation of mobile computing devices as it requires less power and supports a greater number of DPI (dot per inch).
Low temperature polysilicon also allows electrons to move faster than conventional displays, resulting in bright screens capable of higher resolutions.
Indeed, polysilicon displays are so legible and light that e-books are now becoming as easy to read as their printed counterparts.
Plasma displays
Plasma displays offer a wide-angled, brightly coloured viewing experience that is rich and lifelike. But what makes plasma displays so exceptional?
The emissive displays use electrodes to excite the gas plasma, which then causes phosphors in each sub-pixel to produce coloured light (red green or blue).
These phosphors are in fact used in conventional CRT devices, such as televisions and standard PC monitors. However, plasma displays eliminate the need for the long CRT picture tube, instead a digitally controlled electric current flows through a matrix to the pixels where it is required.
Users should, however, take note that plasmas are not ideal for notebooks as they are subject to image sticking and do not currently support resolutions higher than XGA, which is at this stage perfect for digital TV viewing.
Digital light processor
We`ve all seen the large image displays at exhibitions, modern art installations or stage productions. Rock concerts in particular use video walls to project larger than life images of an artist or band`s performance.
DLP (digital light processor) is the latest of these "massive" display technologies and compares favourable to others as it offers bright images, even in low ambient conditions, and does not suffer from screen burn-in.
Using mirrors to reflect light, DLP panel incorporates a DMD (digital mirror display) chip so that the "fairest image of them all" appears on the video wall.
The DMD chip is covered with thousands of miniature mirrors. When a signal is sent to turn a pixel on, a tiny mirror rotates to reflect light towards the screen. When the off signal is sent, the mirror tilts so that the light is reflected away.
From LED to OLED
Most of us are familiar with the humble LED (light-emitting diode) - a semiconductor device that emits visible light when an electric current passes through it.
OLED refers to a broad category of organic LEDs displays. Compared to LCD, OLED is an emissive technology that does not require a backlight and has the potential to eliminate the glass substrate in a display, as well as offer fast response times and a wider viewing angle.
This technology promises thinner, lighter display panels that consume less power than conventional LCDs.
Although this technology is still under development and relatively costly, it may one day replace LCD technology.
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