A monitor is the primary output device for a computer. The two main types of monitors currently in use are Liquid Crystal Display (LCD) also known as flat panel display, and the Cathode Ray Tube (CRT). Each has advantages and disadvantages.
Most older monitors today use cathode ray tube technology, which was first developed for use in television sets. The cathode is a negatively charged electrode that shoots a beam of electrons towards a positively charged electrode, known as an anode. The cathode ray tube is a vacuum tube containing one or more electron guns (cathodes) at one end, which fire a stream of electrons at a screen at the other end. The inside of the screen is covered with a matrix of dots composed of phosphorescent material, known as phosphors. When the phosphors are struck by electrons, they emit light. Phosphors are organized in groups of three, known as a pixel. Each pixel contains a dot that emits one of the three basic colors: red, green, and blue. Magnetic coils in the tube control the direction of the electron stream, and a control grid determines the color combination on the screen. The electron stream starts at the top of the screen moving from left to right, line by line to build an image.
An LCD monitor uses a layer of liquid crystal material sandwiched between two grids of electrodes, one arranged in columns, the other in rows. These grids in turn are enclosed by a layer of polarizing material made out of plastic or glass. These polarizing layers are aligned so as to prevent light from passing through when the electrodes are not activated.
To generate an image, light is passed through the first polarized layer. As the light passes through liquid crystal material, the polarity is changed to allow it to pass through the second polarized layer. This is done by manipulating the electrode grids. The pixels are formed by liquid crystal cells that change the direction of light passing through them in response to an electrode grid.
LCD monitors today most commonly used what is known as thin film transistor technology (TFT), in which a transistor is placed at each intersection of the electrode grids, enhancing the signal and therefore the picture quality. This is also known as active matrix display, as opposed to the older technology known as passive matrix display.
Characteristics to Consider when Choosing a Monitor
There are many features to be considered when choosing a monitor. Some of the more important ones are: screen size, resolution, dot pitch, refresh rate, and response time. Screen size refers to the diagonal length of the screen surface. Resolution refers to the number of pixels that the monitor can display, for example 640 x 480, which indicates 640 pixels horizontally by 480 pixels vertically. The more pixels displayed, the sharper the image. Dot pitch is the distance between dots, expressed in millimeters, such as .25mm, with the smaller the number the better the image. The refresh rate for CRT monitors, or response time for LCD monitors, is the speed at which a monitor builds an image. The quicker the response time or refresh rate, the better the image.
LCD Monitors vs. CRT Monitors
Generally speaking, LCD monitors take up considerably less space than a CRT monitor and are lighter. In addition, LCD monitors use less electricity. However, they are usually more expensive, although this may be partially offset in the long run by the reduced electricity usage.
CRTs usually have higher refresh rates than the response times of LCD monitors, which reduces eyestrain and may be preferable for those who spend a great deal of time in front of a computer. CRT monitors can display at several resolution settings, while LCD monitors use only one resolution, called the native resolution. This can present a problem for high end gaming and graphics displays.
While LCD monitors were initially higher in price and lower in quality versus CRT monitors when they first came out years ago, the technology has improved drastically and LCD monitors now compare favorably in price and display quality to CRT monitors. LCD monitors are the monitors of the future and will eventually make CRT monitors obsolete. For more advice from PC World on how to choose an LCD computer monitor click here.