A high contrast ratio is a desirable feature on any display. By definition, contrast ratio measures the luminosity of the brightest and darkest color that an LCD can display. If a display has a poor contrast ratio there will be a lack of true black and desaturated colors.
There are a variety of methods that can be used to measure a display's contrast ratio and each of these methods can provide a wide array of results for the same display. A typical contrast ratio may be noted as 1000:1 or 100:1. The larger number will result in the best contrast. Display manufacturers and designers prefer different methods of measurements.
Manufacturers measure the contrast ratio based on methods that isolate the display from the system, whereas, designers prefer methods that allow them to factor in the room effect. Ideally a room absorbs all light and the only light displayed would be from the monitor, however, in actual rooms some of the light is reflected back to the display which effectively decreases the contrast ratio.
To further complicate contrast ratio measurements, one must consider both static and dynamic contrast ratios. The static ratio only considers luminosity levels at a single instance in time, whereas, the dynamic ratio considers the luminosity the monitor displays over a period of time. This may be thought of more simply by referring to the static ratio as measuring a static image and the dynamic ratio by considering the affects of a more dynamic or moving image.
Ideal Room Measurement
This type of measurement is typical of manufacturers because it results in the highest possible contrast ratios. This is done by keeping the room at optimum conditions so that the reflective light remains constant. Testing in this manner has no affect on luminance levels, however, it does inflate the light levels.
Real Room Measurement
Contras ratios are more realistic when measured in real rooms that expose the display to conditions where some light is reflected back to the display. ANSI contrast simultaneously measures luminosity values using a checker board patterned test image.
Optimal and Degraded
The Ideal Room Measurement (full on/full off) measurement method effectively measures the dynamic contrast ratio of a display, while the Real Room Measurement (ANSI contrast) is best used to measure static contrast ratio.
Comparing dynamic and static contrast ratios is similar to one trying to compare apples and oranges. These items should never be directly compared. Some manufactures choose to market only the dynamic contrast ratio when the result is better than the display's static ratio. A display with a static contrast ratio of 10000:1 is a much better display than one with a 10000:1 dynamic and 5000:1 static contrast ratio when the input signal contains full range of brightness' from 0 to 100% simultaneously. However the displays will be equal when the input signal range is decreased to a 0 to 20% brightness level.
In order to achieve optimum contrast ratio results, displays are typically measured in completely dark rooms. It will be nearly impossible to achieve these same results during normal viewing conditions. The reduction in contrast ratio will depend on the display luminance and the reflective light in the room.