Btw what do you say to explain HDR to layperson?
I usually says something like this, dunno how accurate / inaccurate that is
"imagine you are holding a paper. It's white and it's bright right? Look up, and you also can see a bright white lights.
Which one is brighter?
Yep. Despite both paper and light are white, the light is brighter.
A good HDR TV will allow you to see that in movies, just like real life."
HDR by itself doesn't define how bright a TV or monitor must be, unless you're talking about VESA standards like "HDR400" which say your panel must be able to output at least 400nits for compliance, but that's a different story.
HDR video (not to confuse with HDR image capture like you have on cameras and smartphones) brings an additional set of data that tells the panel how bright each zone or each pixel is supposed to be in a given scene.
Say a scene where you're inside a cave looking at the exit with a bright, sunny day outside, like this one:
In a typical (SDR) setup, the image/video stream and the TV / monitor will normalize the brightness for the whole picture by making the cave's interior appear much brighter, and the sky much darker.
In reality, if you were standing where the picture was taken, you'd know that the cave's interior is a lot darker and if you were looking at the bright sky through the exit you'd probably even need to squint a bit for how bright it was. I'm guessing you're not squinting while looking at this picture through your monitor / TV / phone.
So there's always been a lot of brightness information lost, which was okay until recently because display technologies weren't capable of showing different levels of brightness within a single frame. All you have on regular LCD panels is a single backlight that defines how bright each frame is, not how bright each zone within each frame is.
Enter OLED panels and LCD panels with local dimming and the TV is now able to show different levels of brightness on the same frame. The cave's interior can be shown with low brightness, while the blue sky can be shown with high brightness, and no color information needs to be lost.
HDR also helps a lot in reducing
e.g. color banding because there's now more bits to define color itself.
Now, as for the brightness part, in truth you'll need a display that can output a bright image or HDR won't be able to do much. That's why VESA is mandating minimum levels of panel brightness for their HDR mode compliance levels, or there's little to no point in supporting HDR at all.
And on TVs and monitors, cheap models that "support" HDR but have no local dimming will simply just accept 10bit color that will reduce banding and little more, ultimately being incapable of showing different levels of brightness.
In the end, don't think that a low-cost "HDR" TV with low brightness and no form of local dimming will inherently be able to show you a better picture than the TV you might already own.
And as for PC monitors, there's little reason to waste money on the HDR tag as all but
the ultra expensive ones will have a single backlight with no local dimming, or just edge lit which isn't great.
For sane prices on PC monitors, just get one with decent brightness and refresh rates instead, or pay ~1000€ for a 55" LG B9 which is the lowest you can pay for an OLED that just happens to be future-proof with HDMI 2.1 support.
