Digital LCD screens first became popular several years ago when they were introduced as lighter, slimmer alternatives to CRT computer monitors. The differences were dramatic. When used to form a LCD HDTV they are even more so.

LCD's produce an image by projecting a light onto a series of 'liquid' crystals sandwiched between glass rectangles. Those crystals can pass or block light as they twist internally. Not really a fluid, the term comes from the fact that the crystals can twist easily when subjected to an electrical current. Varying the voltage changes the amount of twist, which results in the majority of the rear projected light being blocked.

That curious bit of physics gives LCD's their great advantages and introduces some hurdles for manufactures trying to produce great pictures at affordable prices.

The rectangles making up the screen are arranged in rows of pixels ('picture elements') and are actually composed of three, colored sub pixels set side by side. That close spacing and the precise control of twist allows designers to produce an image with great resolution, accurate color reproduction and astounding clarity.

Since every pixel contains the three primary colors needed (red, green and blue) to form any perceivable color, LCD sets can produce a very realistic color image. But doing so requires that 'behind the scenes' the pixels filter the white fluorescent backlight projected onto them.

That arrangement leads inherently to attractive, bright images that plasma type sets cannot quite match. However, as sets age, that backlight can dim or change color, reducing their advantage.

Some LCD HDTV sets offer the option of replacing the backlight, but that can be expensive. Current models have good lifetimes, though, and by the time it becomes a problem many will be looking to replace the set with the latest technology.

LCD's retain that bright, clear image better than most plasmas even under varying light conditions. Both types perform well in darkened rooms, but LCD's have a slight advantage under brighter conditions and more room arrangements. Inherently anti glare, these sets look great in almost any situation.

For several years, plasma dominated the upper reaches of size, while LCD often outperformed in the smaller 13 inch to 37 inch range. With improved technology, both types do well, with LCDs now available as large as 65 inches. Of course, the bigger the screen the larger the price tag.

During those same years, Plasma HDTV sets held the advantage in viewing angle. The nature of LCD panels makes them lose some contrast and the ability to project deep blacks as the viewer moves to the side. Images can look gray and 'washed-out'. Even colors can shift subtly.

Current LCD HDTV sets have reduced that problem to a minimum so that under most viewing conditions it will be unnoticeable. For several years 130 degrees was about the best one could hope for, but 160 degrees or more is common today. That covers a field that would satisfy just about any normal setup.

LCD HDTV sets offer a wide range of uses. In the morning they may serve as a great looking computer monitor, in the afternoon as a game console and in the evening make a first rate LCD HDTV set. Older models struggled with motion blur. For instance, games and some films or shows require 12-15ms response times to avoid streaking. However, current offerings have largely overcome motion blur.

The playing field for LCD HDTV vs Plasma HDTV has leveled to a significant extent the last few years. Today, except for the extreme sizes, the choice comes down primarily to price, reliability and that ever elusive 'best picture' quality. Be sure to 'test drive' any set you consider under good lighting conditions with a quality source.