Introduction to Contrast Ratio: Contrast ratio (CR) is a parameter stated for all HDTVs, but is often very misunderstood. Before the flat panel revolution, CRT televisions never advertised this figure. The answer is simple and lies in the technology. CRTs use an electron beam to illuminate phosphors on the screen and create a picture. If the electron beam is switched off, that section of the screen turns absolutely black. White areas would max out the electron beam. Theoretically, old school TVs had an infinite CR, and blacks were displayed to perfection.
LCD HDTV Contrast Ratio: Modern lcd tvs use twisted nematic crystals to create the picture. What does that mean? Quite simply it is the same as using horizontal window blinds to allow or block light. Each tiny cell on your monitor has sub cells with red, green and blue polarizers. Each cell is controlled by a transistor (TFT is Thin Film Transistor) and thus the perceived intensity of the bright backlight can be controlled. To create black, the cell is ordered completely shut. The problem is (as with the horizontal blinds) that some light will always bleed thru the crystals. This undesirable effect produces blacks that are somewhat gray and even colors that don't seem to pop. Inexpensive, bargain brand LCDs may suffer from this problem. Most people however do not notice this issue until it is pointed out to them.
CR Measurement: LCD makers are free to measure CR in any way that they please. There is no current standard and it is incorrect to compare contrast ratio between manufactures. Basically CR is measured by taking a light intensity reading of the brightest area vs the darkest area on the screen. If the brightest area of the screen is 2500, and the darkest area 10, you have a 250:1 CR. Of course, how you set brightness, contrast, etc. on the TV can have a big impact on these measurements. Also, equipment calibration and setup can have a bearing. Finally, your eyes will perceive contrast differently based on ambient light settings. Do you ever wonder why movies turn down the lights? That should give you a big clue. Also, do not buy a glossy screen if there is ambient light in the room. If you are going to be watching TV in a room with windows and sunlight, opt for a matte screen.
Dynamic CR: Despite the large contrast ratio numbers advertised, bare panels may have CR figures in the 1000:1 range. However, by manipulating back light intensity based on actual scenery, TV makers can get six and seven figure contrast ratio measurements. For example, why run the back light on full intensity when you are looking at the night sky with stars? Dim the bulb, and less light will bleed through the black area giving the illusion of a much higher contrast ratio. Almost all lcd tvs sold now have dynamic contrast ratio. When you purchase a TV, look for contrast ratios above 40000:1 and a dynamic CR number. One last word, dynamic contrast ration isn't a perfect solution, sometimes you have a very dark scene with a small portion of the screen very bright (like a moon lit night). A scene like that could make the difference between a great TV and a mediocre one.
LED Lighting: A new advance in technology uses clusters of LEDs to illuminate the screen instead of a single lamp running the top length of the TV. The Samsung UN55C7000 is an example of such a TV. These TVs can create total blackness in certain areas of the screen, theoretically creating a near infinite (or seven figure) contrast ratio. Because the CR is so high, these TVs can create life like 3D images that appear to lift off the screen!
What should you consider when buying an HDTV? Do not make contrast ratio a major purchasing point. As a rule, look at contrast ratios in factors of ten. A TV with a 600K:1 CR is probably better than one with a 60K:1. Do not simply choose a TV because the CR is a few thousand higher. Read Reviews and pay attention to tag words like black and shadow detail, color vibrancy and even descriptions on how games look. These are the real factors in determining ultimate shadow detail and LCD performance.
