Peak brightness is an important aspect to consider when purchasing a monitor. Not only does a high peak brightness make it easier to work in well-lit environments, but it also helps deliver a better HDR experience because it can produce brighter highlights and more vivid colors. In this article, we show how we measure peak brightness in SDR and HDR, why it matters, and what to look for so that you can make the best buying decision for your setup and needs.
There are mainly two reasons to get a monitor with a high peak brightness: to combat glare in well-lit environments and produce brighter highlights in HDR. Along with high peak brightness, it's essential that the brightness is consistent across different content, especially when image accuracy is required. In HDR, a high brightness makes highlights pop more and helps produce more vibrant colors.
Before measuring the peak brightness, we warm up the display by displaying moving content, usually a video game clip, for 30 minutes. There are three main parts to the test: real scene, peak, and sustained brightness. While we test the real scene peak brightness with a video (shown below), the peak and sustained brightness tests are performed with five different slides. Each slide displays a white rectangle occupying a specific amount of screen space: 2%, 10%, 25%, 50%, and 100%, as shown below. All tests are conducted with the monitor's brightness set to max, and local dimming enabled (if applicable). We perform the tests in SDR and HDR because some monitors get significantly brighter in HDR. The SDR peak brightness measurements are taken after calibration, but the HDR measurements are taken un-calibrated.
To test a monitor's peak brightness, we use a PC to display the SDR test images. For HDR, we use a Samsung Blu-ray player to play the real scene video, but use a PC with Vertex to display the slides. We use a Colorimetry Research CR-100 Colorimeter to measure brightness. The Octave software is used to gather the results for the peak and sustained window tests. The real scene test results are gathered using CRIapp and Excel.
As mentioned above, we measure the real scene brightness using the video clip, and we focus on the lamp at the upper left corner of the screen for 30 seconds. A large percentage of the scoring is based on the real scene peak brightness because it's the one that best represents real-world usage. A peak brightness above 300 cd/m² is considered good and enough to overcome glare in most instances, but you might need higher if the monitor doesn't handle reflections well or if there's direct sunlight shining on the screen.
We perform the SDR peak and sustained brightness tests to see whether there's any brightness variation when displaying different scenes. The peak windows show how bright the monitor can get in the 2%, 10%, 25%, 50%, and 100% windows when the image is only displayed for a short time. The sustained windows show the brightness in the same windows, but for a longer period. Although it isn't as indicative of real-world usage as the real scene measurement, the peak and sustained windows show exactly how bright the display can get, and whether there's dimming in any particular window. Generally speaking, a monitor with consistent brightness is best, especially when image accuracy is required, like for content creation.
The HDR real scene test is the same as in SDR. We use an HDR version of the same video clip, which gives us a more realistic representation of the monitor's brightness in HDR content. We set the monitor to the appropriate HDR mode with brightness at max and enable local dimming (if applicable). We play the video clip and focus on the lamp in the upper left corner to take the measurement. A real scene peak brightness over 550 cd/m² is considered good enough for gaming in HDR, but not for a true cinematic HDR experience, which requires 1000 cd/m².
We measure the peak and sustained brightness in HDR the same way as in SDR, using the 2%, 10%, 25%, 50%, and 100% slides.
Automatic Brightness Limiter is a feature that changes the brightness according to the content displayed on the screen. It's intended to prevent damaging internal components when displaying large, bright images. The ABL test shows the amount of brightness deviation in the sustained windows. We calculate the coefficient of variation using the measurements in the sustained windows, but because the human eye is better at noticing luminosity changes in a dark environment than in a bright one, we first linearize the measurements for any noticeable differences in luminosity using the Perceptual Quantizer (PQ) EOTF, making the results more representative of what is actually perceived. For example, a change of 20 cd/m² is much more noticeable when viewed in the dark than in a bright setting. Most monitors have low or no ABL at all, so this test accounts for a small percentage of the overall score.
There's not much that you can do to improve a monitor's peak brightness other than increasing the brightness and choosing the picture mode that gets the brightest, although these picture modes tend to sacrifice image accuracy. Some monitors have an 'Eco mode' that's intended to reduce power consumption, so you need to make sure that it's disabled if visibility is an issue. 300 cd/m² is usually enough to provide good visibility in most environments, but if there's sunlight or the monitor doesn't handle reflections all that well, then you might want to find one that's closer to 400 cd/m² or brighter. As for HDR, the brighter the better, although there are very few monitors that get bright enough for a true HDR experience. Lastly, when looking at specifications, the advertised brightness can be in 'cd/m²' or in 'nits', which are the same thing.
Except for some budget options, most monitors get bright enough for use in well-lit environments. However, keep in mind that brightness can vary slightly from one unit to another, and the manufacturer's advertised brightness is an estimate that tends to be on the optimistic side. If you're in a room with sunlight or want a better HDR experience, then you should specifically check the monitor's SDR and HDR peak brightness measurements to make sure it satisfies your needs.