Brightness refers to the maximum luminance of a TV. A higher brightness means the TV can make the picture look brighter, which can help with visibility in a bright room.
For these tests, we take measurements of the brightness of a few white rectangles in SDR, each covering different sizes on the screen. The measurements are in cd/m², also known as 'nits'.
Brightness matters in any situation in which you want the picture, or part of the picture, to get really bright. Usually, this applies to one of two scenarios:
If your daily use applies to either of those situations, it's important to get a TV that has high brightness. As you can see in the pictures below, these are two TVs with excellent reflection handling but different brightness. A TV with high brightness results in a more vivid image that's easier to see than one with low brightness.
Our testing for SDR brightness is fairly straightforward. We use our calibrated settings for the TV while setting the backlight/brightness setting to max and using the recommended local dimming setting. We use a Konica Minolta LS-100 Luminance Meter to measure the brightness with different content.
We use a video and five test pictures to measure the brightness in SDR. The real scene video is supposed to represent content in most shows or movies with bright scenes. Also, the test windows, especially the smaller ones, are meant to test for small highlights.
The SDR Real Scene Peak Brightness test is most representative of real-world use. Before playing the video, we 'warm up' the TV so that the pixels aren't 'cold' for this test; almost like an athlete stretching their muscles before physical activity, it's important to get the pixels going before the test. We use the luminance meter and focus on the lamp in the upper-left side of the video for 30 seconds to get our final measurement. Anything above 365 cd/m² should be good enough to combat glare in well-lit rooms. Also, the final luminance measurement can vary up to 20 cd/m² between measurements.
Our peak window tests measure the maximum brightness of a white rectangle displayed on an area covering a certain percentage of the TV’s screen. This provides an idea of how bright a small highlight—the sun, a distant explosion, etc.—might look on-screen, but the larger areas can also represent very bright areas, like if you're watching something with a bright sky.
We use the same setup as the real scene test and measure the brightness immediately after the white square appears on-screen. This is because the TV is the brightest at this point. We repeat the test with the five white slides shown above, each representing different types of content.
We measure the SDR sustained window with the same test images as the SDR peak window, but the only difference is that we test for brightness after the window has been displayed for a few seconds. This allows the TV to 'stabilize' its brightness and is more representative of content with bright areas that stay on for an extended period, like on a hockey broadcast. Luckily, many TVs don't get much dimmer when a highlight stays on the screen longer.
TVs use algorithms to limit how bright the screen gets, especially with large areas, like in our 100% peak window test. It's done to prevent the entire screen from getting too bright and damaging internal electronics. What this essentially means is small areas get brighter than large areas, and we want to know just how much difference there is between the two. Our Automatic Brightness Limiter (ABL) coefficient variant calculates the difference in brightness between the sustained windows tests after normalizing for noticeable differences with the Perceptual Quantizer (PQ) EOTF. This means we only calculate the noticeable differences that we can see when watching TV.
A TV with an ABL of 0 means that the brightness doesn't change across different content. A high ABL is usually found on OLEDs, as large areas are noticeably less bright on those TVs. Also, it's possible for small highlights to be less bright than larger areas because of frame dimming on some TVs, as seen on the Vizio M7 Series Quantum 2020; in this case, the ABL is also high. ABL isn't something you should worry about too much if you just watch SDR content, as most TVs can maintain a high brightness level in SDR without any ABL.
Unfortunately, there's no way to control the ABL. Some TVs dim less than others do, though. If you watch content with large areas of bright colors, like hockey or brightly colored cartoons, you should look for a model that doesn’t have too much of a decrease in brightness between the 25% window test and the 100% window test. Some TVs allow you to disable ABL from the service menu, but we don't recommend doing this, as ABL is designed as a protection mechanism for the TV. Disabling ABL could cause your TV to overheat.
For the ABL calculation to be significant, it should correspond to the way we perceive different luminosity levels. The eye is much more sensitive to small changes in luminosity in a dark environment than in a bright one. Although the measured change in luminosity may be the same, the brighter source is better because we don't notice the change in brightness as much. Essentially, if a screen goes from 25cd/m² to 20 cd/m², it's more noticeable than a screen going from 100 cd/m² to 95 cd/m². This linearization is done with the PQ EOTF, as you can see below.
PQ is a function that relates luminosity with noticeable differences in brightness. When the PQ curve is divided into 4096 segments (12-bit), there are smaller steps that relate to the change in brightness; the horizontal dotted lines represent each step, and as you can see, the first step in each segment represents a higher change than the last segment. We use this to linearize all of our luminosity measurements for this test, ensuring the ABL best represents what's seen.
You should set your TV’s backlighting/brightness to whatever level looks best in your room. Generally, you should keep it a bit dimmer when watching in a dark room and make it very bright in a room with lots of light. Adjusting the luminance of the TV doesn't affect picture quality, so you can easily put it to whatever setting you like.
At the end of the day, you're the one watching TV, so if you want to make the image brighter, do whatever it takes to make it look better for your viewing experience. These are just generalized recommendation settings, and it changes between TVs.
A TV's brightness indicates how bright images can get on the screen. It matters most if you watch TV in a well-lit room, as you want your screen to get bright enough to combat glare; otherwise, it may be hard to see. We test for a TV's brightness to know exactly how bright it can get, but also to see if it remains a consistent brightness level across different content. If you watch TV in dark rooms, then brightness shouldn't be something to worry about.