HDR Nits are a Lie: It’s Time to Embrace the Stop

While maybe a little outside my normal adventures in old school analog video, I wanted to jump way ahead in time to modern video technology. Specifically, I want to talk about HDR TVs and monitors, the use of nits as a measurement, and how peak brightness doesn’t tell the whole story.

HDR is the new “buzzword” in TVs and monitors. About 10 years ago it was all about “HD”, then it was “4k”, and now it’s “HDR”.

First, I want to give a really quick run down of what HDR is, for those who are not familiar with it. HDR stands for High Dynamic Range. In music, we talk about Dynamic Range as being the difference (the range) of the softest parts of the song and loudest parts of the song (the dynamics). This is the exact same concept for video, except instead of volume, it’s brightness. So the dynamic range of video is the difference in brightness (volume) from the darkest black to the brightest white. If that dynamic range is particularly large, we say its dynamic range is high, thus we get the term “High Dynamic Range”, or HDR for short.

So how much dynamic range are we talking about here? Well, that depends on two things: how dark the black is and how bright the white is.

To discuss brightness, we need a brightness unit. There are lots of units of brightness, such as foot-candles, lumens, candelas, lux, and more. But today we are thinking in terms of Nits. Nits are a measurement of light output. The more nits, the brighter.

For black, that’s easy. Black is always defined as zero nits (well, it’s a little more complicated than that, but more on that later).

White is where the big changes happen. On older televisions and monitors, pure white is 100 nits. On HDR monitors, that number changes. Often times, HDR videos are mastered for either 1000 nits, 4000 nits, or 10,000 nits. However, most TVs and devices can’t get that bright. Instead, they just get as bright as they can, call that white, and lower the dynamic range of the content accordingly. This is a process called Tone Mapping and is a complex discussion for another day.

So, this means that the brighter the TV the better right? Or at least, so it would seem. If black is always zero, brightness is clearly the most important thing, no? Well there is more to it than that. But first, let’s see what sort of numbers the manufacturers brag about. To keep things as even as possible, I’m only looking at 65 inch, HDR, UHD TVs, plus one crazy “pie-in-the-sky” professional monitor.

Brand	Model	Peak Brightness in Nits (as measured by RTINGS)	MSRP (in USD)	Display technology
Samsung	Q60T	476 nits	$999.99	Quantum Dot LED (QLED)
Samsung	Q70T	488 nits	$1299.99	Quantum Dot LED (QLED)
Samsung	Q80T	739 nits	$1799.99	Quantum Dot LED (QLED)
Samsung	Q90T	1407 nits	$2499.99	Quantum Dot LED (QLED)
LG	B9	603 nits	$2299.99	WRGB OLED
LG	CX	813 nits	$2499.99	WRGB OLED
Vizio	P659-G1	634 nits	$999.99	Quantum Dot LED (QLED)
Vizio	PX65-G1	2373 nits	$1299.99	Quantum Dot LED (QLED)
Sony	BVM-X300 V2	1000 nits*	$35,000.00	RGB OLED

Okay so what’s going on here? How is that Vizio PX65-G1 the same price as the Samsung Q70T, but nearly five times brighter? Why is LG’s flagship CX the same price as Samsung’s flagship Q90T, but nearly half as bright? And lastly, why is that Sony display so insanely expensive but it’s brightness only middle of road?

Obviously, there is more to a TV or monitor than just how bright it is. There are lots of other factors at play like color reproduction, sounds quality, and more. But still, you would think that brightness would correlate directly with price, especially because, as we established, it’s one of the key things that defines a screen’s dynamic range.

But that’s just it. Brightness is one of the key things that defines a screen’s dynamic range. The other thing is black level.

This is where stuff gets a little complicated. You see, most screens can’t show true black. In fact, OLED and plasma screens are the only screens that can show a true black image as really black. Try this out: pull up a black screen (credits in a movie are a good place to start) on any LCD screen. This could be your TV, phone, tablet, or another device. You’ll notice that the screen is still glowing a little bit. It isn’t true black. While technically, true black should always be 0 nits, in the real world, it rarely is. Because of this, dynamic range is actually worse on those TVs with a higher brightness black.

“Now surely the difference in black level can’t be very much, right?” You might ask. You might be thinking that even if the black level on the worst TV is, say, two nits, and on an OLED or plasma, it’s zero, that’s only a two nit difference. Some of the TV’s in that chart have brightness differences over 1000 nits model to model. So why does the black level actually matter when it’s such a tiny difference? Well, we’ll get there, but we need to stop thinking in terms of brightness and nits. We need to look at how camera folk measure dynamic range.

Camera folk don’t think about dynamic range as nits the way TV and monitor manufacturers do. Instead, they think of it in term of Stops. A stop is a halving or doubling of light. So, if you have two light bulbs and one is twice as bright as the other, you could say the brighter one is “one stop brighter” or the dimmer one is “one stop darker”. If the bulbs are 4 times different in brightness, they are actually only two stops apart: the darker one is the brightness of the brighter one cut in half, and then cut in half again. That makes it two stops dimmer.

For one last example, if the brighter bulb is 24 times brighter, it would be 4.5 stops brighter than the darker one. This is because if the dim bulb is one unit of brightness, we could double it to two units (that’s one stop), double it again to four units (that’s two stops), double it again to eight units (that’s three stops), double it again to 16 units (that’s four stops), and then we need to bump it up by 1.5 times to get it to 24 units. Since that last bump was only a 50% increase and not a 100% increase, it’s only a half stop, giving us a total of four and a half stops.

This is a really useful way to measure dynamic range because it’s a lot closer to how our eyes work. We don’t perceive brightness linearly; we perceive it logarithmically.

Digital cameras, like TVs and monitors, have a fixed dynamic range. That is to say, they have a limit of the brightest thing they can capture and the darkest thing. Anything beyond that limit will be maxed out and be turned into solid white or solid black and lose all of its details.

Now I can hear some of you thinking “but I can change a digital camera’s ISO! You can’t change a TV’s ISO! That makes all this comparison worthless”. First of all, if you don’t know what ISO means, don’t sweat it. You can safely skip this paragraph. For the rest of you: no. You actually can’t change a digital camera’s ISO. A digital camera sensor’s ISO is fixed. This fixed ISO value is called its Native ISO. Any changes you make to ISO in your camera’s settings are simply an estimate of what that ISO would look like by artificially brightening or darkening the image. This is analogous to push or pull processing of a film stock. You can process 800 ISO film as 1600, but that doesn’t make it 1600 ISO film stock. Don’t believe me? Try this out: use a digital camera that can shoot RAW and take a picture of something really bright, like a very bright light bulb (don’t take a picture of the sun because you’ll cook your sensor). Shoot wide open on your fastest lens with a kind of slow shutter speed. Obviously, the picture will be totally blown out. “But wait!” you say, “I shot RAW so I can lower the ISO in post!”. Try it. It’ll still be blown out, but it’ll be gray with no detail instead of white with no detail. Even if you set your ISO to a mythical 0.001 you still won’t get any detail. You might get more detail out of something that looks to be blown out on your display (say, a cloud), but that’s because the image wasn’t actually clipped to begin with. Your display is what was clipping. When you lower the ISO, you are simply dropping the brightness of the image down into your screens “window” of possible dynamic range. Your camera’s ISO settings are a lie.

But anyway, I digress. Camera dynamic range is static and unchanging, just like a screen’s. Therefore, we can think of a screen as a sort of camera in reverse: instead of absorbing light it emits it. This means that we can use stops to measure a screen’s dynamic range as if it were a camera.

Now, this is a little challenging to do because:

1. OLED and plasma screens can turn off individual pixels (a true, 0 nit black). Since zero times zero is still zero, we need to use the brightness of the darkest shade the screen can produce before turning all the way off as our starting point. The same goes for LED/LCD TVs that use local dimming to produce true black.

2. The black level in nits is not something normally measured and I don’t own the equipment necessary to measure it myself. Therefore, we must rely on theoretical numbers. With this in mind, we’ll be using the black level numbers put in place by the UHD Alliance. They state that LCD/LED TVs reach about .05 nits, and OLEDs can get down to 0.0005 nits.

So, let’s look at that same table from earlier, with the estimated black level and dynamic range in stops:

Brand	Model	Peak Brightness in Nits (as measured by RTINGS)	Estimated Black Level, based on display technology	Estimated Dynamic range in stops.	MSRP (in USD)	Display technology
Samsung	Q60T	476 nits	0.05 nits	13.2	$999.99	Quantum Dot LED (QLED)
Samsung	Q70T	488 nits	0.05 nits	13.3	$1299.99	Quantum Dot LED (QLED)
Samsung	Q80T	739 nits	0.05 nits	13.9	$1799.99	Quantum Dot LED (QLED)
Samsung	Q90T	1407 nits	0.05 nits	14.8	$2499.99	Quantum Dot LED (QLED)
LG	B9	603 nits	0.0005 nits	20.2	$2299.99	WRGB OLED
LG	CX	813 nits	0.0005 nits	20.6	$2499.99	WRGB OLED
Vizio	P659-G1	634 nits	0.05 nits	13.6	$999.99	Quantum Dot LED (QLED)
Vizio	PX65-G1	2373 nits	0.05 nits	15.5	$1299.99	Quantum Dot LED (QLED)
Sony	BVM-X300 V2	1000 nits*	0.0005 nits	20.9	$35,000.00	RGB OLED
N/A	Hypothetical Perfect screen, adhering to existing HDR standards	10,000 nits	0.0005 nits	24.3	N/A	Hypothetical

Now we can see some clear patterns. The OLED screens have really high dynamic range, despite their lower peak brightness because they have such good performance on the black end. All the OLEDs are within 1 stop of each other, and all the LEDs are within 2.5 stops of each other. We also can see that the screen with the best dynamic range is our monstrous $35k broadcast monitor, even though it isn’t the brightest. When compared to the theoretical limits of existing HDR standards, it’s less than 3.5 stops away from perfection.

Furthermore, lets continue our camera comparison and look at the dynamic range of several cameras used in professional filmmaking.

Brand	Sensor	Camera Models	Dynamic Range in stops
ARRI	ALEV III	ALEXA Classic family, AMIRA, ALEXA Mini, ALEXA XT family, ALEXA SXT family	14
ARRI	A2X	ALEXA LF and LF Mini	14
ARRI	A3X	ALEXA 65	14
RED	MYSTERIUM	RED One	11.5
RED	MYSTERIUM-X	RED One, DSMC1 family	13
RED	DRAGON/DRAGON-X/DRAGON VV	DSMC1 and DSMC2 families	16.5
RED	GEMINI	DSMC2 family	16.5
RED	HELIUM	DSMC2 family	16.5
RED	MONSTRO VV	DSMC2 family	17
Sony	Super35 Single Chip CMOS	F5, F55, F65	14
Sony	35mm Full Size CMOS	VENICE	15
Kodak	Vision3 5219	N/A	~14
N/A	Computer Renderings, adhering to existing HDR standards.	N/A	24+

What can we learn from this? Well, we can see that LCD/LED screens are barely hitting the dynamic range the cameras filming the content can capture. The OLED screens, on the other hand, can.

This means that nits don’t tell the whole story. Dynamic Range is the difference from the darkest black to the brightest white, and for that value to be meaningful, we need to look at both sides of the coin. After all, a doubling of peak brightness is only an increase of one stop. But black level isn’t everything either because you don’t want all your content to be sitting in the near black range where it is nearly impossible to see. Ideally, you want the best performance on both ends of the spectrum.

And again, I want to be clear, dynamic range isn’t everything. There is more at play than just dynamic range. If a TV or monitor is more money than another, there is likely a reason for it. The Vizio PX65-G1 in the chart above has better dynamic range than any of the Samsung ones, but is about half the price of the Q90T. Is the Vizio one poorly made? Is the Samsung one overpriced because of the brand name? Is the Samsung TV better in some other, measurable way? Probably all of the above. This blog post is only looking at why dynamic range should not be looked at as only peak brightness in nits and is not an end all buyer’s guide.

With that said, as one last quick thing before I go, I want to talk a little more about why that $35k Sony BVM monitor is so good. Yes, its dynamic range is impressive at a staggering near 21 stops. But the really important thing is the fact that it is RGB OLED as opposed to WRGB OLED, like what’s found in the LG OLED TVs. The LG OLED TVs are not able to reproduce any color in the very bright end, only shades of white and gray. The W in WRGB stands for White. RGB, stands for Red, Green, and Blue, the three primary colors of light. Red, green, and blue can be mixed to create any color, including white. So WRGB is sort of like saying White+Color. It uses the White to add to the other colors to create something brighter at the sacrifice of color vibrancy. The Sony BVM broadcast monitor, on the other hand, is only RGB. That means that it is blending colors together to create all its super bright images, meaning it can show white as well as rich, vibrant color in the super bright highlights where the WRGB LG OLED TVs simply can’t. It is truly as close as you can get to “a camera in reverse”, thus the high price tag.

So, in summary, nits are only good for measuring brightness of something, but brightness doesn’t translate to “good HDR”. Rather, good HDR is all about the difference between the blackest black and the brightest white, and the ratio between them. By understanding this, we can get a much better sense of what a truly good HDR monitor or TV is, and by comparing them to what today’s cinema cameras can do, we can really get a good feel for how much it matters in the real world.

Photo credit: Sony a7R III Sensor photograph by Tony Webster, licensed CC-BY-2.0 https://creativecommons.org/licenses/by/2.0/ . No changes were made to the photograph.