The contrast ratio is the ratio between the luminance of the brightest white and the darkest black that a monitor can produce. Higher contrast ratios typically mean deeper blacks, which makes a big difference in overall picture quality. It’s of particular importance for dark scenes in movies and games, especially in a dark room.
To test contrast, we measure the luminance of both white and black and then calculate the ratio between the two. Luminance is a metric used to measure the amount of light (or intensity) present on a surface and is expressed in cd/m², or candelas per square meter. This is commonly referred to as "nits".
The contrast ratio is one of the most important aspects of picture quality, as images generally look better if blacks are really black and whites are really white. This is especially noticeable in a dark room, when watching movies or playing games with dark scenes. On a PC, this can also be noticeable if you use your computer's dark mode, as the user interface elements won't be truly black on a monitor with a poor contrast ratio.
In a bright room, a higher contrast ratio isn't as important, as the reflected ambient light reduces the perceived difference you might get with deeper blacks, so higher contrast ratios aren't as beneficial.
Even in a dark room, small differences in contrast usually aren't very noticeable. Generally, a contrast ratio difference of 500 is considered to be a noticeable difference, but above a certain point, even this won't be very noticeable.
When displaying a black image on an LED TV, some light is always lost. To measure the contrast ratio, we need to measure the amount of light the display is emitting when displaying pure black, and compare it to the amount of light emitted from pure white.
Once we've measured the black and the white luminance, we're able to calculate the contrast ratio. To get this number, we divide the white luminance by the black luminance.
Because it's a ratio, there is no unit for contrast. Instead, contrast is normally expressed as ‘X : 1,’ with ‘X’ being how many times brighter white is than black. For example, a 5000 : 1 contrast ratio would mean that the television emits white that is five thousand times brighter than its black. The higher the contrast ratio, the deeper the blacks and the better the picture will look.
The 'Native Contrast' represents the most basic contrast ratio of the monitor, with the least amount of image processing added, and any features designed to improve the contrast ratio disabled, like local dimming.
To measure the native contrast ratio, we use a black and white checkerboard pattern to determine the black and white luminance, as described above. We calibrate the monitor to have a white luminance as close as possible to 100 cd/m², and then we take five luminance measurements using an LS-100 luminance meter.
The white luminance, which should be close to 100 cd/m², is measured in the center white square. For the black luminance, we measure the luminance of each of the 4 black squares surrounding the white center square. This is to reduce the impact of black uniformity on our contrast measurement. The final black luminance number is the average of these 4 squares.
Once we have both of these values, the contrast ratio is simply the white luminance divided by the black luminance.
The 'Contrast with Local Dimming' test is nearly identical to the 'Native Contrast' test, but this time, we measure the contrast ratio with the monitor's local dimming feature enabled. On monitors with multiple local dimming settings, we use the setting we recommend, based on the results of our 'Local Dimming' test. In most cases, this is the highest setting available.
Most monitors don't have a local dimming feature, so for most of our reviews this is set to 'N/A'. Local dimming on monitors is expected to become more and more common, especially as HDR displays grow in popularity.
Since we only measure the SDR contrast ratio, on some monitors it isn't possible to measure the contrast ratio with local dimming, as local dimming is only available in HDR. This is pretty rare though.
As a first step, try using the calibration settings we recommend (provided we have reviewed your monitor). This will get good, basic contrast - meaning no additional contrast-enhancing settings - and with no loss of detail in dark portions of the image. You can find this information in the 'Post-Calibration' section of the review.
Most monitors also have a few other settings that affect contrast. We listed a few below, along with our thoughts on whether or not they should be used.
There are different ways to measure contrast. We measure contrast with a checkerboard pattern and take the average black level from four squares, but some other review sites measure it differently, which can lead to a difference in posted numbers. Some of the other methods we've seen websites use include:
Because of differences in measurement techniques, equipment used, and even differences between units, it's extremely common for different websites to report slightly different contrast measurements.
Monitors use different display technologies, each with advantages and disadvantages. Knowing which type of panel is used in your monitor can already give you a good indication of what to expect in terms of contrast ratio:
Even within the same panel types, it's normal for the contrast to vary a bit between units, even of the exact same model, due to manufacturing tolerances. Manufacturers used to provide the typical contrast ratio for each monitor, but recently, some brands, including LG, have started listing the minimum contrast ratio you could get. For example, LG lists the 27GL850-B's typical contrast ratio at 1000, but lists the minimum contrast at 700. We measured the contrast on our unit at 735, which is towards the bottom end of their range. Most people shouldn't be concerned about this though, as the difference between the high and low end of the range isn't very noticeable.
A monitor’s contrast ratio indicates the depth of blacks – a higher contrast ratio means deeper blacks – and by extension, better picture quality. It’s a very important part of picture quality, so if you want something that looks good (particularly in a dark room), be sure to get a monitor that has good contrast.
There are a few things that can be done to improve contrast, but there are limits. As a good first step, look to our recommended picture settings (listed with every review), as those can help you get a good baseline. From there, you can enable or disable a few different settings that might help deepen blacks. Just remember that some of those settings will have other consequences on picture quality.