When looking at HDTVs, you may have noticed that the contrasts on the devices range from "2000:1" to "35 000:1". Rather easy to choose you may think, but not really, and this is why.

Simple explanation

There are two different types of contrast (seems everything about HDTV is more complex than one could imagine), Dynamic contrast, and Static contrast.

Static contrast (2000:1)

This is the lower ratio, it compares the white and the black on the same picture/screen. Basically how much brighter is the white than the black. This is sometimes known as ANSI (use of black and white check boxes on the same screen).

Dynamic contrast (35 000:1)

These are the higher contrasts, and it also compares the white and black, but does it on separate pictures/screens. For example they will have a solid black screen and then a solid white screen, and then compare how much brighter the white is than the black. Also known as Full ON/OFF.

A little more tech
Contrast is the difference of the brightest and the darkest measurements on a screen. These light measurements are called the luminosity and are measured in candelas (cd/M²). For example if a bright spot is 500cd/M² and a dark spot is 0.50 cd/M² the screen will have a contrast of 500:0.05 = 1000:1.

Conclusion
If possible compare Static contrast. To compare between different manufacturers, put the two screens next to each other in the shop, and ask them to play a bright scene, and then a very poorly lit scene. If you really want to be clever, take a CD you know has bright and low lit scenes, and use that instead of their "picture perfect" CDs. Don't exclude checking with their Blu-ray CD disks - soon all homes will be using Blu-ray (High quality picture and sound). Remember the lighting in your home will never be the same as the shop, but this should give you a good idea.