When comparing TVs of today to the models of yesteryear, the biggest difference between the two is the widespread ability to read an HDR signal. The question then asks itself, how big is the impact of HDR? Does it make previous TVs obsolete?
Unlike the upgrade from 1080p to 4k, the difference between the two bears no relation to the environment the TV is watched in. The biggest factor is the picture quality of the TV itself since what HDR actually is is a new, more precise way to describe what the TV needs to display.
HDR is an initialism for High Dynamic Range. The term has been used for a long time now but nowadays when talking about HDR video; it is entirely about metadata. Well, what is metadata then? HDR metadata is simply additional information sent with the video signal. This information is complete color descriptions that the TV can read and then display precisely. Metadata is then distributed through two different standards, HDR10 and Dolby Vision. While this is the only parameter required to support HDR, TVs also need to reach other requirements to make use of this additional information and show a difference.
Think of it this way: With SDR, a car would be ordered to apply "full throttle" or "50% throttle." Instead, the HDR car would be asked to "go to 120 mph" and "go to 40 mph." Some vehicles would provide a worse experience than others working towards this task, and most might not even succeed. TVs are the same. In the past, the signal would be a level of power, while on HDR, it is a specific set goal.
The latter is set beyond what current TVs are capable of, requiring levels of brightness and colors the display might not be capable of reproducing. With HDR, TVs with higher peak brightness and wider color gamuts gain a purpose. Flagship models are capable of getting closer to the requirements and offer a more accurate picture compared to lower end models with limited performance in these aspects.
For the purpose of this test, we will compare two different TVs over three scenarios: A high-end TV fed an HDR signal, the same TV being sent an SDR signal, and a mid-range HDR TV in HDR mode. For the SDR signal, we used an HDFury Linker and replaced the TV's EDID with one that hid HDR support effectively making the player think it was connected to an SDR TV.
A TV that supports a wider color gamut is capable of displaying a palette of colors with more saturation than a standard TV. While this isn't a necessity for HDR, they go hand in hand. In the past, even if a TV was capable of supporting one, almost all of the content was produced to fit into a smaller color gamut.
As you can see in this comparison, there is a noticeable difference between HDR and SDR, mostly in the greens and reds which are where most of the expansion went towards. However, you can also see that this isn't inherently a factor of HDR. There is little difference in color saturation between the SDR picture and the low-end HDR one. Since a lot of budget HDR TVs lack a wide color gamut, they will see no benefit from this aspect of HDR.
Winner: HDR, but only on a TV with a wide color gamut.
Much like color gamut, color depth refers to the different colors a TV can display. The difference between the two can be a bit confusing. Color gamut refers to the level of saturation the TV can display, while color depth refers to the number of colors the TV is capable of showing within that palette. A limited color gamut would stop a TV from displaying the red of an apple accurately, while a limitation in color depth would make the red gradients on that apple look uneven and with visible steps.
What is commonly called an 8-bit TV will have 256 shades of red, green and blue or about 16.7 Million in total. This seems like quite a small amount when compared to 10-bit TVs which would have 1,024 shades of each channel or 1.07 Billion colors.
Color depth affects gradients the most: a TV with a lower bit depth will have to spread it over a far smaller amount of steps. A limited bit depth can lead to blockiness and uneven gradients, which you can often see on skies like on the SDR picture above. This is one of the rare cases where the HDR related features on the lower-end TVs will find a purpose since most of them have a 10-bit panel nowadays. Unfortunately, it's the least visually impactful one.
Finally, we take a look at dynamic range. This is where an HDR TVs will show the biggest difference. HDR content makes use of their higher brightness capabilities to show lifelike highlights. When a TV has a limited dynamic range, it can only display highlights while crushing the dark elements and vice versa. A TV with higher dynamic range is capable of displaying more of both at the same time. Peak brightness, contrast as well as the quality of the tone mapping have the biggest impact on this aspect.
The difference is visible on the X930D, one of the brightest TVs we've tested this year. The amount of detail resolved in the sky and the mountain in the background is better than in the other two examples, all while maintaining detail in the shadows under the cars. The difference can still seem minimal, though, and that is both because capturing it with a camera is impossible and because even the best TVs of today barely scratch the surface of what HDR brings forward.
Winner: HDR, but only if peak brightness is high enough to be noticeable.
In the grand scheme of things, HDR is a great advancement in the world of TVs. It however only just started to gain traction. Current TVs, even the flagship ones, don't really make much use out of it. You won't gain much visually from having an HDR signal sent to a mid-range TV since any picture quality enhancements are reliant on the capabilities of the set itself. High-end models do see a benefit, but it's a limited one (see our recommended HDR TVs). If you bought a good TV recently and you were thinking about upgrading for HDR support, it's not worth it just yet.