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WHAT THE STANDARDS SAY

Brighter highlights,
deeper shadows.

4K is about more pixels. HDR is about better light.

A dark living room at dusk with a large wall-mounted television showing a bright sunset over the sea, the glow lighting the sofa — AI-generated image, not a photograph of a real person or place.

High dynamic range widens the gap between the darkest and brightest parts of a picture, so sunlight glints and shadows keep their detail. Two formats in one international standard do it in very different ways.

STOPSnot pixels

Compare the ranges

Keep in mind

Range, not resolution
Nits measure brightness
PQ and HLG differ
Light, measured properly

THE SHORT ANSWER

More range,
measured in stops.

Each stop is a doubling of brightness.
HDR adds many stops to what standard TV can show.

THE GAP

Standard TV is narrow

BBC R&D says conventional 8-bit SDR television has a displayed dynamic range of about 32:1, or 5 stops. HDR is designed to go well beyond that.

Compare the ranges

THE UNITS

Nits are candelas

Absolute brightness on screen is measured in candelas per square metre, also called nits. The PQ format describes every pixel in these units.

See the numbers

THE FORMATS

Two kinds of HDR

ITU-R BT.2100 defines PQ and HLG. HLG, invented by the BBC and NHK for broadcasting, needs no mastering metadata and adapts to the screen.

How they differ

HOW MUCH RANGE?

From 5 stops
to 28.

Pick a system to see how much dynamic range it covers, according to BBC R&D. The bar shows the size of the range.

Range check

Choose a systemStandard TV (8-bit SDR)Your eyes, in one sceneHLG (10-bit)PQ (10-bit)

Standard TV (8-bit SDR)About 5 stops

A displayed dynamic range of about 32:1. Printed pictures manage only slightly more, about 6 stops, because of how black ink reflects.

Your eyes, in one sceneUnder 14 stops

In any one scene the eye sees about 10,000:1. Across starlight to sunlight it adapts over a far bigger range, roughly 0.0001 to 100,000 cd/m².

HLG (10-bit)About 16 stops

On the final display, depending on black level. That comfortably exceeds what the eye can see in a single scene.

PQ (10-bit)About 28 stops

Far more than cameras, displays or the eye can use in one scene, because PQ encodes absolute brightness up to a peak of 10,000 cd/m².

Source: BBC R&D, Frequently Asked Questions on High Dynamic Range and Hybrid Log-Gamma (December 2016).

A stop is a factor of two in brightness, so 5 stops is about 32:1.

TWO NUMBERS WORTH KNOWING

Where white sits,
and how high PQ goes.

One figure for everyday white,
one for the ceiling of the PQ format.

203 cd/m²

Reference white on a 1000-nit HDR display

In HLG, reference white sits at 75% of the signal and shows at 203 cd/m² on a 1000 cd/m² display. In PQ it is about 58% of the signal and always 203 cd/m² on a reference display.

REFERENCE WHITE · BBC R&D 2026

10,000 cd/m²

Peak brightness the PQ signal can describe

PQ is an absolute, display-referred signal with a peak of 10,000 cd/m². When the target display is dimmer, only part of its signal range is used.

PQ PEAK · BBC R&D

So everyday whites in HDR sit near 200 nits. The headroom above them is for highlights and specular reflections, while shadows keep extended detail.

FOUR THINGS TO KNOW

Reading HDR
without the jargon.

No shopping advice here: just what the terms on screens, streams and settings menus actually mean.

A broadcast control room with rows of colour monitors and a mixing desk, seen from behind an anonymous operator — AI-generated image, not a photograph of a real person or place.

Step 1

Separate HDR from 4K

Resolution counts pixels; dynamic range is the span from dark to bright. A picture can have one without the other.

Step 2

Read 'nits' as brightness

A nit is one candela per square metre, the unit used for absolute brightness on a display.

Step 3

Know the two formats

PQ describes absolute brightness; HLG describes relative scene light and lets each screen adapt it.

Step 4

Expect broadcast HDR to be HLG

HLG was designed for live TV, works without metadata and is royalty-free in ITU-R BT.2100.

PQ VERSUS HLG

Absolute light,
or relative light.

A close-up of a television screen showing sunlight sparkling on rippling water, with deep shadows under nearby rocks — AI-generated image, not a photograph of a real person or place.

PQ is display-referred: the signal says exactly how bright each pixel should be in nits, HLG is scene-referred, like conventional television: it records relative light levels in the scene, and needs no metadata describing the mastering display.

BBC R&D says it chose that design because metadata often gets lost or out of sync in a live broadcast chain. HLG also has native compatibility with standard dynamic range UHD displays and works with existing 10-bit infrastructure.

Questions

Questions on the way

What does HDR mean on a TV?

High dynamic range. It uses the capability of modern displays to show pictures in high contrast, with bright highlights and specular reflections plus extra detail in shadows, according to BBC R&D.

What is a nit?

A nit is one candela per square metre, the unit for absolute brightness on a screen. PQ is currently the only absolute video signal in widespread use.

Is HLG limited to 1000 nits?

No. BBC R&D says HLG is a relative system not aimed at any particular brightness; 1000 cd/m² is simply a typical capability of professional HDR monitors.

Which standard defines HDR TV?

Recommendation ITU-R BT.2100, the international standard for HDR programme production and exchange. It defines PQ and HLG; the current version, BT.2100-3, was approved in February 2025.

Does HDR look the same on every screen?

Not exactly. Displays and rooms differ, so pictures are adapted. HLG can be graded on one monitor brightness and shown on a brighter or dimmer one with essentially the same perceptual look.

Destination

Where the facts come from

Updated 16 October 2026

Brighter highlights,deeper shadows.

More range,measured in stops.