HP L2035 User manual

LCD vs. CRT Displays for Professional Graphics
Applications
Introduction......................................................................................................................................... 2
Image quality ...................................................................................................................................... 2
Other benefits of LCD technology .......................................................................................................... 3
Future development.............................................................................................................................. 4
Summary ............................................................................................................................................ 5

Introduction
Over the past few years, the computer industry has experienced a rapid shift from the traditional CRT
monitor to those based on liquid-crystal display (LCD) technology. As of late 2004, the LCD
accounted for over half the PC monitors shipped worldwide, the latest milestone in a trend which is
expected to continue through the decade. This will soon result in the CRT being relegated to use only
in low-end applications and emerging markets, where cost is the primary concern. The effects of this
trend on the display industry have also been readily apparent, as many long-time CRT makers have
ceased production of this type of display and turned their full attention to the LCD. This has been of
particular concern in the high-end computer graphics market, where a relatively small number of
manufacturers have supplied the large-size (20-22" diagonal) CRT monitors used in CAD, CAE,
computer animation, and other professional graphics-intensive fields.
In the past, this market has been dominated by "aperture-grille" CRT types, some of which are now
reaching the end of their production life, at least in this segment of the market. This situation is raising
concerns in many customers' minds regarding their future display needs. Will there be suitable
alternatives to these familiar CRT monitors? Can LCDs meet the demanding needs of this industry?
Fortunately, LCD technology has been developing at the same rapid pace that LCD monitors
themselves have been gaining market share. Driven by the demands of both the computer monitor
and television markets, today's LCD monitors provide greatly improved color, brightness, contrast,
viewing angles, and response time, and at a lower cost than their predecessors of just three or four
years ago. The current state of the art in LCD products can equal or better CRT performance in
virtually every area, while still providing the LCD's traditional advantages of reduced size, weight,
and energy consumption. In addition, LCDs have always lacked many of the deficiencies which
traditionally plagued CRT monitors—such as uneven focus, imperfect linearity, and color
misconvergence and purity problems. This paper provides an in-depth look at many of these issues,
including some advantages of the LCD which may not often be considered in the average display
purchase decision.
Image quality
As noted above, the LCD cannot suffer from many of the image problems which have always affected
CRT displays (and which could never be completely addressed in that technology). The LCD, like most
other "flat-panel" display types, is a fixed-pixel technology. When operated in its native mode (as is
generally recommended), the LCD display provides a one-to-one correspondence between the
"logical" pixels which create the image in the computer and the physical pixels on the display screen.
Each pixel is in precisely the proper relationship to the others, completely eliminating any concerns
over linearity, geometric distortion, focus, or other alignment or distortion problems. Objects within
the image are assured of being displayed at the correct size and shape no matter where they appear
on the screen. This is especially important in critical applications such as those being considered here,
and even more so with large-screen (20" and above) monitors—where relatively minor distortions are
that much larger, and where the CRT has always been particularly vulnerable; larger CRTs are in
general more difficult to properly correct than their smaller kin.
In addition to these benefits, the LCD's completely different method of producing its image gives it
significant advantages over the CRT in the areas of color and brightness uniformity and overall
brightness. LCDs essentially operate as "light valves," acting to let a measured amount of light through
colored filters at each pixel location. The light is produced by a "backlight," which is simply a source
of bright white light located behind the LCD panel itself (as seen by the viewer). This arrangement can
produce significantly higher light output, with better uniformity, than was ever possible with high-
resolution CRT displays. The light output of the LCD is also far more constant than that of a CRT,
essentially eliminating any concern with display "flicker" even at high brightness levels and relatively
low refresh rates. An LCD monitor will be flicker-free even at video-friendly frame rates of 50-60 Hz,

unlike its CRT competitor. Again, this is of particular benefit in large-screen displays, as the perception
of display flicker is related to the percentage of the viewer's visual field occupied by the displayed
image.
Two areas in which LCDs have historically been at a disadvantage relative to the CRT are viewing
angle and response time. Here again, developments in LCD technology, driven primarily by the needs
of the consumer television market, have virtually eliminated these concerns. Current LCD monitors
typically offer response times in the range of 12-16 milliseconds, well under the frame time of
standard video and sufficiently rapid to eliminate earlier problems with "ghosting" or "smearing"
within the image.
The LCD still has a different "look" than the CRT, owing to the fact that it is a very stable light
source—a given frame of information appears on the screen and is illuminated at a relatively constant
level until the next frame appears, as opposed to the highly-varying light output of the CRT (which
relies on the persistence of human vision to give the illusion of a stable image).
However, additional features which have been introduced initially in LCD TVs, such as "blinking
backlight" techniques and "black frame" insertion, promise to give a more "CRT-like" viewing
experience without re-introducing the flicker problems of the CRT. These features are expected to be
introduced to the PC monitor market in the fairly near future. Similarly, viewing angles have improved
dramatically since the early days of the LCD, thanks to the introduction of newer LC operating modes,
which, now in the best products, provide a range of 160 degrees or more without loss of contrast or
objectionable color shifts.
One seldom-considered aspect of the LCD's image quality advantage is in the area of stability. CRT
monitors are notorious for drifting out of adjustment over time; the nature of the CRT itself causes this,
as the emissive surface in the electron gun (that part of the tube which produces the electron beam
used to "paint" the picture on the screen) ages and its characteristics change; in simple terms, the
electron gun gets weaker with age. This means that repeated adjustments are required in order to
maintain constant brightness levels and the proper color balance. (In some critical applications, CRT
monitors are calibrated weekly or even daily to maintain consistent performance!)
The LCD does not suffer from this problem; the color filters and backlight , which control the brightness
and color characteristics of the display, are far more stable with time and do not require that the
monitor be recalibrated nearly as often as the CRT, as long as the user adjustments are not changed.
This results in a significant savings in time and labor, and assures the user of a more consistent image
from day to day.
Further improvements in LCD performance are expected in the future, with the introduction of solid-
state (LED) backlighting in high-end display products. This will further improve the reliability and
stability of these products, while greatly expanding their color gamut (the range of colors which the
display is capable of reproducing) well beyond the capabilities of CRT products.
Other benefits of LCD technology
The LCD offers several other advantages over the CRT which are particularly important in large-
screen, high-performance applications. Several of these are obvious—a 20" or larger CRT is a very
bulky, heavy product, as opposed to its thin, lightweight LCD counterpart. Even a 24" LCD can easily
be moved or adjusted by practically any user. The LCD also has a significant edge in terms of power
consumption, generally saving well over 50 percent in electricity costs vs. large-size CRT displays. The
latter can easily consume 150 watts or more each, the equivalent of having a large light fixture
burning constantly at every work position! As a by-product of lower electricity consumption, the LCD
will also produce less heat—which can be a significant problem with installations of multiple CRT-
based displays.
The depth and weight advantage of LCDs is especially pronounced when comparing "widescreen"
displays (i.e., those with a wider aspect ratio than the traditional 4:3—"wide" displays may offer an

HDTV-like 16:9 or 16:10 image). In a CRT monitor, the depth of the tube is directly related to its
diagonal size—so a "wide" CRT must be deeper than a standard tube of the same height. Large-
screen wide-aspect CRT monitors wind up being very large and heavy products, and the wider
screens also have a more difficult time maintaining convergence, focus, etc.—whereas the LCD has
no difficulties at all as a wide-format display, and very large, wide screens can be produced that are
still thin and relatively lightweight.
Other advantages of the LCD are not as often considered, but may be equally important. One major
example is the fact that the LCD is not a significant source of electric or magnetic fields, nor is it
affected by such fields as may be present in the ambient environment. CRT displays, which use
magnetic fields to control the electron beam and a very high voltage supply to accelerate the beam,
may emit strong fields which can interfere with other equipment in the area, and are also notoriously
susceptible to externally-produced fields.
Local magnetic fields from AC power lines or even nearby AC-powered appliances can distort the
CRT's image, cause problems with color purity and convergence or even induce visible "jitter" into the
image. The LCD is completely immune to such fields, and in fact is the only display technology
suitable for use in many industrial or medical applications for this reason. Susceptibility to external
fields increases with screen size, which makes this issue again of even more importance when
considering large-screen displays.
Future development
Additional development of LCD technology is continuing, and is expected to soon address those few
remaining areas in which the CRT still offers an advantage. At this time, the CRT's remaining strong
points are its low cost—it remains the most cost-effective display device, and will for some time—and
two aspects of image performance: the response curve, or "gamma," of the display, and the black-
level luminance. The cost advantage of the CRT, as noted, is likely to continue for the foreseeable
future—although LCD prices will also continue to decline as additional large-area production capacity
is brought on-line by the LCD makers. However, we must also again note that the number of CRT-
based options in the high-performance segment of the market is declining rapidly, and CRTs will very
likely leave this portion of the market completely while remaining the low-cost alternative in other
segments.
The response-curve differences between the LCD and CRT are being addressed as new drive systems
(and true 10-bit LCD drivers) enter the market, and improvements in the black-level luminance (which
basically is a question of "how black 'black' looks"—especially in a low-ambient-light environment)
are also expected to be coming in the near future. These additional developments will leave little
doubt that the LCD has truly arrived as the display of choice for critical high-end applications.

Summary
To summarize, current large-screen LCD monitors offer the following advantages over their CRT
counterparts:
•Essentially perfect linearity, "focus," and geometry; a precise, one-to-one match exists between the
pixels of the image and those on the screen*.
•No color purity or misconvergence problems.
•No need for frequent recalibration or adjustment as compared with CRT requirements.
•Excellent color and brightness uniformity.
•A bright, stable, high-contrast, and flicker-free image.
•Reduced monitor depth and weight at all screen sizes, particularly for "widescreen" displays (and,
in general, less variation in the display's "footprint" on the desk).
•Significantly lower weight; easier positioning/adjustment of the monitor.
•Lower power consumption.
•No significant electric- or magnetic-field emissions and no susceptibility to external fields.
*When the LCD is operated at its native format, or "resolution."
These features have already combined to make the LCD the dominant display in the overall PC
monitor market, and the latest products now make this technology a very good choice for demanding
high-end graphics use. As the CRT exits this portion of the market, today's high-performance LCDs are
ready to meet the needs of the graphics professional.
© 2005 Hewlett-Packard Development Company, L.P. The information
contained herein is subject to change without notice. The only warranties for
HP products and services are set forth in the express warranty statements
accompanying such products and services. Nothing herein should be construed
as constituting an additional warranty. HP shall not be liable for technical or
editorial errors or omissions contained herein.
5983-0982EN, 02/2005