Currently, flat screen TVs are created using two different technologies: Plasma and Liquid Crystal Display (LCD). The foundation of the plasma TV is over a million tiny glass cells that are charged with a mixture of neon and xenon. Behind these cells are colored phosphors, which are chemical compounds that emit light when energized.
Each cell has three phosphors; one red, one blue, and one green. When activated by an electrode, the plasma cells emit invisible UV light.
The UV light strikes the red, green and blue phosphors on the back of the display and thus creates the pixels that form the image you see on the screen. LCD (Liquid Crystal Display) technology works differently. Liquid is suspended between two transparent panels. Within the liquid are crystals that, when activated by voltage, re-position themselves so that they either allow the light to pass through the panel and or block the light. This process is similar to turning on and off a million light bulbs. Fluorescent tubes behind the panels supply the light source. Both the lit and unlit crystals create visible pixels that cumulatively compose the image on the screen.
Pros and Cons of Each
Brightness in LCD and plasma screens is typically expressed as candelas per square meter (cd/m2). Typically, plasmas are listed at 500-700 cd/m2, but independent reviewers say that that the brightness of plasma is closer to 100 cd/m2. Conversely, LCD TVs typically get a brightness rating of 450 cd/m2, again when measured independently.
Contrast ratio is the measurement of the brightest white against the blackest black that the TV can create. The higher the contrast ratio, the easier it is to discern details on the screen. Current plasmas measure contrast ratios of up to 3000:1. However, independent reviewers believe that measured in real world viewing situations, contrast ratios for plasma TVs drop to approximately 200:1. Conversely, LCD TV contrast ratios range from 350-450:1 when measured using the same realistic standards.
Color saturation describes the amount of grey in a color. The more grey, the lower the saturation. Plasma has the advantage over LCD in the area of color saturation because of it's method to light blocking. Plasma is able to completely turn off pixels when not in use, so that no stray light dilutes the colors. The way LCD technology works means that there is some stray light and therefore obtaining true color is difficult.
Right now, the plasma market offers TVs as big as 60 inches, and no plasma TV is available smaller than 32 inches. LCD screen sizes range from 13 inches to 46 inches, and because of manufacturing innovations, larger models are becoming available every year. Look for LCDs to catch up in this area soon.
Historically, plasma TVs have had a larger viewing angle, at about 160 degrees, when measured against older LCD TVs. However, the newer model LCD TVs have viewing angles up to 175 degrees.
Burn in is what happens when an image stays on a plasma screen for an extended period of time. LCD's are not at all susceptible to burn in. While Plasma TVs are vulnerable, some newer plasma TVs have added features that combat it.
Typical plasma TVs have a life span of 20,000 to 30,000 hours, which equates to at about 20 years of usage if you have the set on for 4 hours a day. The lifespan of an LCD TV is typically 50,000 to 60,000 hours, or about 40 years running 4 hours daily.
Response time is the amount of time, measured in milliseconds (ms), that it takes for a pixel to go from active to inactive and back to active again. Lower numbers mean faster transitions and fewer visible image artifacts. Plasma TVs were made to handle rapid movement on the screen more effectively. They can have response times as low as 15 ms. LCD TVs started as PC displays, and so the need to show fast movement wasn't critical; somewhere around 25 ms. LCD manufacturers have been steadily improving their response times as the demand for fast moving, full motion video has increased. Newer model LCD TVs can have response times as fast as 16 ms.
Because the crystals in LCD TV do not produce light, the technology is labeled as "non-emissive," which means it does not give off radiation like the CRT. Cold cathode light sources, like fluorescent tubes, which use only a little power, are used to illuminate the image. LCDs also use less power than plasma televisions, because plasma requires powering hundreds of electrodes to stimulate the phosphors.
Knowing that flat screen TV is not going away, there is no time like the present to start enjoying all the advantages that these new technologies. But keep an eye on the new kid on the block - OLED.
Questions? Visit the Tech Talk Radio forum, and we'll be glad to answer them or email us directly.
For more information - see Plasma Myths.