LCD DISPLAYS

12/7/2002

LCD Displays are flat panel displays built as arrays of backlit Liquid Crystal elements. LCD displays have a number of advantages over the older CRT technology. They weigh less. They occupy less space. They generally require less power. At one resolution they can precisely display 1 element per pixel. They have a true flat screen with no distortion at the sides/corners. Magnetic and Electric field levels around the display should be much lower than CRTs and they are unaffected by external magnetic fields. Unlike CRTs, LCDs do not require refreshing many times a second and should not exhibit flicker interactions with AC electric lighting unless the material being viewed is itself interacting with the lighting.

The disadvantages of LCDs include cost; marginal intensities; occasional failure of display elements; poor visibility and color alteration off axis with some technologies; limitations on speed of changing intensities; and poor resolution except at the one resolution where the screen and display resolution match one for one. Some users report an optical illusion wherein the center of the flat screen appears to be depressed. LCDs do not offer color ranges as wide as CRTs, but in most cases, the difference will not be noticeable. Fast moving objects may show artifacts at their edges when viewed on LCD monitors due to slower fade times. Low resolution pictures may look "grainier" on LCDs than on CRTs.

Matching one pixel per display element requires direct digital drive of the LCD rather than converting the display to analog using a conventional video card, then converting back to digital. This is generally provided in laptops, but not in desktops. Display cards that provide direct LCD drive are uncommon, likely to be expensive, and may not include the analog drive required for CRT monitors.

Although the intensities of the best LCDs appear on paper to approach those of CRTs, the measurement techniques are different. CRTs have a substantially greater brightness range between the brightest displayable white and the faintest viewable image. LCDs are improving, but as of late 2002, they are still less satisfactory than CRTs in very bright lighting and do not have brightness ranges as broad as CRTs. It is possible to increase LCD brightness by using a brighter backlight, but this is not done in consumer products. Another consideration is that LCDs screens are generally less reflective than CRTs. Reflections can be a problem under certain lighting conditions -- especially direct sunlight.

Both CRTs and LCDs have normal lifetimes of a number of years.

There are a number of LCD technologies in use with a variety of capabilities and limitations. Thin Film Transistor technologies that became affordable around 2000 offer performance that is comparable to CRTs when viewed more or less straight on in typical office environments.

Diagonal measurements on LCDs give a much better indication of viewable area than those on CRTs which often offer viewable diagonals only about 90% of the advertised size. A 12 inch LCD has roughly the same viewable area as a 14 inch CRT. The largest LCDs readily available as of late 2002 have 24 inch diagonals. There is rarely much choice of resolution for a given screen size of LCD. Typically a given diagonal measurement will only be available in one or two native resolutions. For example, a 15 inch LCD (equivalent to a 17 inch CRT) will probably only be available in 1024x768 resolution. Although lower resolutions will be supported, they may only use a portion of the screen real estate, or may have variable column widths.

Some fonts may not reproduce well on LCDs -- especially older ones. The "standard" Windows fonts are virtually unreadable on some older laptops and must be replaced with vendor supplied fonts.

Return To Index Copyright 1994-2002 by Donald Kenney.