Contrast
Ratio is the difference between the whitest white and the darkest
black colors that the display can show. Generally speaking, the
greater the contrast the better the screen and the subtlety of colors
it can display.
Contrast
ratio is often used when describing TVs. A high contrast ratio,
such as 4000:1, signifies a better color representation (bright
images will appear better against a darker background) than a lower
contrast ratio, such as 2500:1. A 3000:1 contrast means 3000 times
brighter than black. Typically, you want to purchase a projector or flat-panel
TV with a high contrast ratio. Below are examples of
different contrast ratio's.
Low
Contrast
When contrast is low, images appear washed out. Parts of the image
may become difficult to see clearly. Projectors with contrast ratios
of less than 500:1 typically provide low contrast.

Simulated
image of low contrast
Medium Contrast
When a projector provides good contrast, images are clear and attractive. Projectors with contrast ratios ranging from 500:1 to 1200:1 typically
provide medium contrast.
Simulated image of medium contrast
High Contrast
With high contrast, images are ultra crisp with vibrant colors.
Projectors with contrast ratios exceeding 1200:1 typically provide
high contrast. DLP TM (DDR) technology projectors currently offer
these high contrast ratios. Additionally, some LCD projectors are able to offer high contrast ratios as well.
Simulated image of high contrast