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SCREENS. They’re everywhere. Televisions. Computers. Cell phones. E-book readers, Smart phones. Tablets. Each of these devices requires that the user view a screen to input and view data. They are called screens, monitors, displays, tablets and many other names, but they all serve the same purpose: To show the user the data within the computer.
But, of course, it isn’t that simple. There are many different types of screens. This is primarily because these ubiquitous color displays consume considerable battery and electrical power the more they are used. And each new generation of smartphone, tablet and computer finds more and more ways to suck up energy - viewing movies, playing games, video phone calling. So the goal is to constantly provide the clearest possible display with the longest possible battery life.
How is this done? One way is to keep the display in black and white (like the Kindle e-book reader) and not color (like, for example, the Nook). Another way is to increase the battery size and speed up the charging process. Also, by changing the battery type (e.g. from NiCad to LiOn), increasing efficiency. But by far the best process has been the steadily progressive technology, making the screens thinner and less power hungry.
The original TVs and computers relied on the bulky, heat-emitting cathode ray tube (“CRT”) technology. These displays required full electrical power and could not be used with batteries. Essentially, the CRTs shoot an electron beam through a vacuum at a glass screen, the interior of which is coated with phosphors. As the beam passes through a magnetic field which varies in strength according to an electronic “display controller” and then a mask (or “mesh”) which defines the individual pixels and the resolution on the screen (either an “aperture” grille (thousands of holed) or a “shadow mask” (vertical slots)), the electrons are sorted by colors (reg-green-blue, the so-called “phosphor triad”) and the individual phosphors light up in analog color, which is interpreted by the video card for display.
CRTs became extinct when users discovered LCD screens, the thin, light and cool monitors that made room on a desk and looked sleek rather than clunky. Generally, these screens were lumped into the description “Flat Panel Displays.”
LCDs, short for Liquid Crystal Display, became immediately used on watches, TVs and computer monitors. Developed in 1963 at RCA’s Sarnoff Research Center in Princeton, NJ, LCD displays use two sheets of polarizing material with a liquid crystal solution sandwiched between them. When an electric current is passed through the liquid, the crystals allign so that light cannot pass through them. Each crystal is like a shutter, either allowing or blocking light. Color LCD displays use two basic techniques for producing color: Passive-Matrix (including CSTN and DSTN technologies); and the much more popular Active-Matrix (a/k/a thin-film transistor or “TFT”). Most LCD screens used in laptop computers are backlit, or transmissive, to make them easier to read. Most popular these days in phones and computers are TFT-LCD screens, which usually have four layers: a backlight, a TFT color filter, a touch-sensor panel and an outer glass screen.
Naturally, LCD screens have different considerations from CRTs. First comes “contrast ratio.” This is a comparison of the brightest possible white compared to the darkest possible black, expressed as a ratio. The higher the ratio, the better the screen. This becomes necessary because the backlight on the screen can’t filter out all of the light for a true black, which sometimes appears more gray, while turning down the backlight will conversely make the black blacker while reducing the brightness of white at the same time. Common ratios are 300:1 to 600:1 for computer monitors (TVs can be up to 800:1 to 1200:1).
In an effort to make LCDs faster, some manufacturers have reduced what is known as “bit depth.” Beware of this if you’re doing graphic design. Normal quality dictates 8 bits of color per RGB channel, resulting in a total of 16.7 million colors. But if the bit depth is reduced to 8 bits, color may be compromised, requiring “dithering,” which is the use of software to “fake” the missing colors. [By the way, this is NOT the same thing as the 32-bit color in your video card and your computer desktop, which is almost always fully usable.]
Next, consider “refresh rates.” Most older monitors have adjustments for this. Refresh rate is the number of times per second that the screen is refreshed. The higher the better. If it’s too low, the screen image starts fading before it’s renewed, causing that annoying “flicker.” 60Hz resolution is a minimum on a smaller screen with less lines to renew, but 100Hz is best on larger screens. However, on LCD screens you should be more concerned with “response time,” which isn’t the same thing. In LCDs, this is the amount of time in which a liquid crystal can twist, then untwist, to either pass or block the light for each pixel. The faster they can accomplish this, the quicker the screen. Response times are stated in milliseconds - below 16ms is pretty good, but you can get and will want 8, 4 even 2 milliseconds if you’re a gamer.
About the same time, PLASMA technology emerged. This plasma display panel (“PDP”) technology is primarily used in large-screen (42” or greater) televisions. Plasma is similar to LCD technology but, instead of liquid crystal, the display is created by thousands of tiny tubes filled by inert ionized gas in a plasma state between the panels to provide the image. Because of this construction, plasma isvery light and flat, permitting handing TV screens directly on a wall.
The next generation of screens, used on laptops, but more on cell phones and TVs, uses light-emitting diodes (“LEDs”) originally used for electronics indicators and low voltage display lighting. A diode is a semiconductor device (a solid electronic component that conducts electricity under specific conditions) that emits light when an electric current passes through it. The light is not terribly bright and ranges in output from red to blue, but is highly efficient, long-lived and requires very low power.
After that, LED technology progressed to the newer, OLED (organic LED), which is a display technology based on the use of an organic substance, typically a polymer, as the semiconductor material in light-emitting diodes. An OLED display is created by sandwiching organic thin films between two conductors. When an electrical current is applied to this structure, it emits a bright light. OLEDs don’t require backlighting, can be thinner and weigh less than other display technologies, offer a wide viewing angle (up to 160 degrees), have less video blur and use less power (only 2 - 10 volts). They are consequently quite popular on TVs, laptops, and PDAs. But they do have some problems with glare and readability in direct sunlight, even relative to LCD screens. To be expected, there have been several types of OLEDs. Just like LCDs, OLEDs can be either AMOLED (“active matrix LED,” where each pixel is driven separately, using two transistors and one capacitor) and PMOLEDS (“passive matrix OLEDs,” which drive the pixels by row and column (x-y) coordinates).
Samsung has recently introduced the Super Amoled screen, which is “super” because the touchscreen display integrates the touch sensors with the glass surface panel, eliminating at least one layer of glass and, with it, a layer of air. It also enhances readability, reducing the glare problems experienced with AMOLED.
There are also several rather expensive technologies in the market, but they have not become as popular as Super AMOLED: Super LCD, Super IPS and Advanced SuperView. Basically, each phone manufacturer uses its screen(s) of choice. You have to select your carrier, then your phone, considering the screen that you think will be best for you.
The newer OLED technology has morphed to include the FOLED (flexible organic LED), which is built into a portable, roll-up display. The newest LEDs are being created using ultrathin inorganic LEDs which are brighter and more versitile (bendable; think human body or building displays).
Even more recently, companies like Plextronics (founded by Richard D. McCullough) have been perfecting electronic “ink,” a flexible polymer that can be printed on anything, even a magazine page.
Finally, there is an entire generation of touch sensitive screens, whether full size ones used for input in business like restaurants, to the smaller smartphone and pad links on modern iPads and iPhones, which allow resizing, typing and selection. (Like the Amoled design shown above.) But the underlying resolution and technology are still based on the distinctions discussed above.
It’s important to have some, but certainly not all, of the information above if you’re purchasing a device with a screen. It matters what you’ll be using it for, how much battery life you’ll require, how much color you need, how clear or bright the display has to be. You may not always have a choice on these matters, as your carrier or monitor manufacturer may not offer everything. But at least you know what to avoid and what the standards are.
Wait for a few months. Something new will probably come along.
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