Definition: contrast ratio

The ratio of the brightest white to the darkest black on a TV or computer monitor. The larger the number, the greater the extremes; for example, car headlights can appear brilliant next to the pitch black of the night sky. Contrast ratio is an important criterion in screen quality.

White Divided by Black
The ratio is derived by the brightest luminance divided by the darkest luminance in candelas per square meter (cd/m²). For example, if white is 98 cd/m² and black is 0.02, the ratio is 4900:1. In the 2013-2014 time frame, and using the same testing method, LED TVs have been measured with contrast ratios from 700:1 to 7500:1.

Following are two of many measurement methods; however, contrast ratios are known to be "invented" because vendors can apply a technique in different ways to come up with higher numbers. One bogus approach is to adjust the TV white level to settings the viewer would never really use.

ANSI Contrast and Full On/Off
ANSI Contrast uses a checkerboard of alternating black and white squares, and the average white output is divided by the average black output. The test may be done by calibrating the white to 100 cd/m² and then measuring the black.

Full On/Off measures an all-white screen with an all-black screen and always produces a higher ratio than the ANSI Contrast. See LED TV, Dolby HDR and dynamic contrast.