Comparative Analysis Of Computer Display Systems
When shopping for a new computer system, consumers tend to agonize over the CPU speed, hard disk size, or memory, but what about the one component of a computer that is equally utilized? The monitor often referred to as a display screen. The monitor is the component of a computer system that displays the messages and data being processed by the computer’s central processor unit. Two of the most common types of monitors are the CRT (Cathode Ray Tube) monitors and LCD (Liquid Crystal Display) monitors. Despite significant differences between LCD and CRT technologies, both types are equally marketable. CRTs are bigger and bulkier than LCDs, consume more power and are prone to screen flicker. LCD monitors, however, are more expensive in relation to CRTs, they introduce the problem of viewing angles, and generally have less accurate color replication.
Each type of monitor has its advantages and disadvantage, the following analysis will provide a comparison of CRT and LCD monitors, along with defining some of the many specifications and terminologies consumers should be aware of when purchasing a computer display system.
1.0 CRT or LCD
Deciding whether to choose LCD or CRT is a difficult question as there are several criterions involved. Depending on the importance of each of the qualifications to the application, final decision will favor either the LCD or CRT.
· Image quality
· Total cost of ownership
· Space consideration
· Available budget
1.1 Image Quality
Which technology offers the best image quality is a complex question. While LCDs presents crisp images, CRTs have superior color clarity, sharp pictures, and fluid video playback capabilities. Unlike LCDs, CRTs display more colors and use emissive technology (meaning that they generate their own light) and, as a result, can be viewed from practically any angle. When you look at an LCD monitor from an angle, the image can look dimmer or even disappear. Colors can also be misrepresented. To compensate for this problem, LCD monitor makers have designed wider viewing angles. (Often confuse with a widescreen display, which means the display is physically wider.) Manufacturers give a measure of viewing angle in degrees (the greater the number of degrees, the better the LCD screen.) In general, look for between 120 and 170 degrees. Because manufacturers measure viewing angles differently, the best way to evaluate it is to test the display in person. Check the angle from the top and bottom as well as the sides, bearing in mind the typical use of the display. (PC World magazine, August 2006)
Table 1 summarizes important image quality differences between the two technologies.
Perfect Geometry Geometric Correction needed
Pixelization due to black lines between pixels Continuous image
Uniform sharpness Less Uniform Sharpness
600:1 contrast ratio (Dark Reading Room) 3000:1 Contrast Ratio (Dark Reading Room)
Contrast Ratio dependent on viewing angle Contrast Ratio independent from viewing angle
LCDs like white CRTs like black
Imperfect Black Perfect Black is possible
Low reflection of Ambient light High reflection of ambient light
Poor Stability (Good with I-Guard) Good Stability
Poor Response Speed Instantaneous response speed
Image Retention No Image Retention
Backlight Aging Phosphor aging
Aging independent of image content Aging is image content dependent
New Technology Mature Technology
Low Power Consumption High Power consumption
No Image Flicker Image Flicker Present
Table 1 Significant Differences Between LCD and CRT Technologies
Source: American Association of Physicists. (2004)
“Assessment of Display Performance”
1.2 Total Cost of Ownership
As the initial investment in flat panel technology is still higher than CRT, one has to look at other factors to verify whether the cost remains in favor for the CRT. The basic reason for price difference is that CRT monitors have developed over the last twenty years with computers and the manufacturers of the CRT monitors have already covered their development and production set up costs. The cost of both technologies has decreased over the past few years, and LCDs are reaching a point where smaller monitors are within many consumers’ price range.
Another financial factor is the power consumption of LCDs, which is about half that of an equivalent CRT display. CRTs consume a lot of power and thus generate a lot of heat. Over the lifetime of an LCD display this will result in energy savings, and lower air-conditioning costs. (Poor, 2002)
There is a general consensus that LCD technology is less critical to failures than the high end CRT technology. The main reasons for this are:
· Lower voltage use
· Lower power consumption
These will result in lower maintenance cost for the displays. LCD backlights can be replaced when the lamps are exhausted. The cost for this is lower than the replacement of a CRT picture tube.
1.3 Space Considerations
It is clear that if space is an issue (which is often the case), LCD technology offers a clear advantage over the bulky and heavy CRT technology. CRTs cubic shaped screen are three times bigger than the same screen size flat screen and generates a waist of work space. For an optimum vision comfort, the distance between the user and the screen must be: 1.5 x the exact screen size diagonal (Kelly, 2005, p. 95). For instance, to properly view a 17” monitor, the right distance should be: 17 x 1.5 = 25.5 in. (Figure 1)
Figure 1 Optimum Vision Comfort Zone
Source: Kyrnin. (2007) “CRT vs. LCD Monitors”
An LCD monitor is significantly thinner and lighter than a CRT monitor, typically weighing less than half as much. Unlike CRT monitors, LCD monitors have much more flexibility for positioning the screen in any way. LCD monitors can swivel, tilt up and down, and even rotate from landscape (with the horizontal plane longer than the vertical plane) to portrait mode (with the vertical plane longer than the horizontal plane). In addition, because they are lightweight and thin, most LCD monitors have built-in brackets for wall or arm mounting.
At this moment LCD technology still comes at a premium price compared to CRT. The initial investment will be higher than using CRT technology. However, it possible to reduce the investment considerably by choosing the right display for the right application. The lower resolution models are substantially less expensive than the high-end models. As the technology matures, further price reductions will make LCD technology even more competitive and perhaps replace the CRT technology.
Budgeting for either type of monitors relies on the intended purpose of the display system. CRT monitors are better suited for consumers who will use the system for desktop publishing, graphics development, and gaming without the need for portability, or those who are on a limited budget. Others who use the computer for word processing, programming or limited desk space should select the LCD monitors.
2.0 Display parameters
We can characterize the displays that are available on the market in a number of categories. Separate categories can be distinguished based on resolution, brightness, uniformity, color, and calibration possibilities.
Resolution on a CRT is flexible and a newer model will provide viewing resolutions of up to 1600 by 1200 and higher, whereas on an LCD the resolution is fixed within each monitor (called a native resolution). The resolution on an LCD can be changed, but if you’re running it at a resolution other than its native resolution you will notice a drop in performance or quality.
Dot pitch refers to the space between the pixels that make up the images on your screen, and is measured in millimeters. The less space between pixels, the better the image quality. (Figure 2)
Figure 2 Magnified view of dot pitch on a CRT monitor
Source: Kyrnin. (2007) “CRT vs. LCD Monitors”
On either type of monitor, smaller dot pitch is better and you’re going to want to look at something in the 0.26 mm dot pitch or smaller range.
Both types of monitors (newer models) provide bright and vibrant color display. However, LCDs cannot display the maximum color range that a CRT can. In terms of image sharpness, when an LCD is running at its native resolution the picture quality is perfectly sharp. On a CRT the sharpness of the picture can be blemished by soft edges or a flawed focus.
2.2 Refresh Rate
In monitors based on CRT technology, the refresh rate is the number of times that the image on the display is drawn each second. If your CRT monitor has a refresh rate of 72 Hertz (Hz), then it cycles through all the pixels from top to bottom 72 times a second. Refresh rates are important because they control flicker, and the faster the refresh rate the better the monitor. Too few cycles per second and you will notice a flickering, which can lead to headaches and eye strain. LCDs are flicker-free and as such the refresh rate isn’t an important issue with LCDs.
Typically, brightness is not a concern with CRT monitors. LCD monitors are backlit and have different levels of brightness. The brightness rating for an LCD monitor is commonly referred to as ‘nits’, and commonly range from 70 to 250 nits. The higher the nits, the brighter the display. LCD monitors offer almost twice the brightness compared to the CRT monitor. If placement of the display system is in a brightly lit room or with plenty of sunshine coming through the window, LCD is the best choice.
Most CRT monitors are capable of displaying unlimited colors. Some LCD monitors are only capable of hundreds or thousands of colors, but many of the newer LCD’s are closing the gap rapidly.
3.0 Summary of Comparison
A monitor is an absolutely essential part of any computer system, selecting a monitor with the size, image quality, and energy efficiency to suit a consumer’s needs is equally important. The falling prices of conventional CRTs are making larger monitors more attractive and affordable. Now the market offers more choice than ever with the emergence of sleek, compact LCDs.
The choice between CRT and LCD technology depends heavily on the application.
CRT display systems are suitable for:
2. Graphic developers
3. Serious video gamers
LED display systems are suitable for:
1. Computer programmers
2. Office clerks
Assessment of Display Performance. (2005). American Association of Physicists.
How Stuff Works, Inc. (1998-2007). CRT and LCD Computer Monitors. Available WWW:
Kelly, S. M. (2000). Flat Panel Displays, Advanced Organic Materials. Cambridge, UK: The
Royal Society of Chemistry.
Kyrnin,Mark. (2006, December). CRT vs. LCD Monitors: Which Type of Monitor is the Best to
Buy? Available WWW:http://compreviews.about.com/library/weekly/aa-crtvlcd.htm.
Liquid Crystal Display (2006, August). Light, Slight, and Stylish- LCD Monitors. PC World,
Poor, Alfred. (2002, November). Displaying the Future. PC Magazine,16-27