An LCD monitor is a thin, light computer monitor that displays images through the use of a liquid crystal display. LCD screens are found in most laptop computers as well as in flat panel monitors, and have replaced traditional cathode ray tube (CRT) monitors for many users. CRTs once were preferred by many users for their superior color presentation; improvements in LCDs have made the difference less noticeable, but still important to graphics and photography professionals and serious amateurs.
Inside the LCD
A color monitor is typically made up of five layers: a backlight, a sheet of polarized glass, a mask of colored pixels, a grid layer of responsive liquid crystal solution, and a second polarized sheet of glass. Images are created manipulating the orientation of the crystals through precise electrical charges of varying degrees and voltages. They act like tiny shutters, opening or closing in response to the stimulus, thereby allowing degrees of light that have passed through specific colored pixels to illuminate the screen.
As LCD technology has evolved, different techniques for producing color have emerged. Passive matrix screens, which were the first invented, use two transistors — one for each row and one for each column of pixels — to activate a particular point on the LCD grid. Active-matrix screens usually use thin film transistor (TFT) technology, in which each point on the grid has its own transistor; this allows only the desired pixels to be activated. Passive matrix screens tend to respond more slowly than active matrix screens, and are not able to produce the same level of image quality.
Most modern LCD computer monitors use active matrix technology. Within this group, there are a number of specifications that set one LCD monitor apart from another. Size, aspect ratio, and resolution are three related features; contrast ratio, brightness, viewing angle, and response time are also important.
The size of an LCD monitor can affect its price, resolution, and aspect ratio. Larger monitors are more expensive; the transistors that are used to make active matrix displays have a high failure rate, and since bigger monitors have more transistors, consumers are paying in part for those that are defective and cannot be sold. Aspect ratio refers to the shape of the screen, with standard screens usually having a 4:3 or 5:4 ratio. Widescreen monitors tend to be bigger, but allow images to be viewed in a 16:9 (or 16:10) aspect ratio.
A bigger screen may also allow for a higher native resolution, or the number of pixels it can display. A screen with a high native resolution will be very sharp, and be able to display more information than one with a lower resolution can. Most monitors can display resolutions other than what is native, but the image may appear blurry.
Contrast ratio relates to the display's comparative difference between its brightest white values and its darkest black. A higher contrast ratio will have truer colors with less washout, and allow for a greater range of shades. The standard offering for lower-end models is commonly 350:1, but many experts recommend a contrast ratio of 500:1 or better.
LCD monitors tend to be bright, with standard levels being more than adequate for everyday use. Brightness is measured in nits, units of one candela per square meter. Anywhere from 250 to 300 nits is standard, although people who play games may benefit from a brighter screen. If the nits are much higher, the user will likely end up adjusting the brightness down for regular use.
The vertical and horizontal viewing angle specifications refer to the degree the viewer can stray from dead center before the picture starts to wash out. Most monitors are looked at straight-on, but wider angles can benefit people who use multiple screens, or if the screen will be used by several people at one time. Many experts recommend a viewing angle of at least 140° horizontal and 120° vertical, but the wider the viewing angles, the better.
Response time is measured in milliseconds (ms) and refers to how long it takes pixels to turn from completely white to black and back again. Smaller values represent a faster response time and are more desirable, especially for playing games and viewing videos. If the response time is slow, ghosting or trailing can occur with fast-moving images, where images linger as the screen refreshes. A maximum response time should be no more than 25 ms for general use, and 17 ms is better. Many gamers report no ghosting using an LCD monitor with a response time of 16 ms or less.
One major advantage of LCD monitors are their size; they are commonly 1 to 3 inches (2.5 to 7.5 cm) thick and weigh less than 10 pounds (4.5 k). CRT monitors, on the other hand, have a depth five times as large, and a weight of 30 to 50 pounds (13 to 23 kilograms) or more. As such, LCDs can take up 90% less space, and are far easier to move or adjust.
A wide variety of screen sizes are available, from 15 to 30 inches (38.1 to 76.2 cm) or larger. For average sizes — 22 to 24 inches (55.88 to 60.96 cm) — the price of an LCD monitor is about the same as a traditional CRT. LCD screens tend to last longer, however; in addition, if a few pixels on the screen fail, the monitor is still usable in most cases.
LCDs use relatively little electricity, especially when compared to their CRT counterparts, and produce far less heat. They also emit very low levels of electromagnetic radiation. LCD monitors are also easier on the eyes; glossy or matte screens are usually available, and matte screens reduce glare.
LCD monitors have largely displaced CRTs in most monitors, except for very cheap and very expensive models. CRTs still can offer better color content and depth at the high end, and also have the advantage of multisync, or the ability to keep colors consistent even when a picture's resolution is changed. Colors on LCDs may also change hue as the viewer moves to the outer limits of the viewing angle, particularly on displays with narrow viewing angles and low contrast ratios. Graphics, photography, and design professionals, as well as medical professionals, usually have preferred CRT monitors for these advantages.
A potential weak link of an LCD monitor is the backlight. Since the liquid crystals do not produce any light on their own, if the backlight fails, the monitor is unusable. Many monitors come with a three-year warranty, but stipulate one year for the backlight.