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Displays

Nits (cd/m²)

A nit is one candela per square meter (cd/m²), the unit for how bright a screen is. A higher number means a brighter image, and spec sheets quote typical, peak and sustained values that can sit far apart.

Typical, peak and sustained

Three different numbers hide behind one unit. Typical brightness is a normal white screen, the level you'd use all day. Peak brightness is what a small bright area can reach in HDR. Sustained brightness is what the whole screen can hold for longer. A spec sheet that says 1000 nits needs a second look to find out which one it means.

Say a monitor lists 250 nits typical and 1000 nits peak. The peak is 4 times the typical figure, but it's measured on a small patch of the screen, like the 8% center patch DisplayHDR uses. A white window that fills the screen won't get there. On OLED, a power limit is the reason.

Where content sits

A brightness number only means something next to what content asks for:

  • sRGB reference white: 80 nits
  • SDR video grading: 100 nits
  • Typical consumer LCD monitors: 200-300 nits
  • HDR reference white: 203 nits, from ITU-R BT.2408
  • HDR displays: about 400-2,500 nits
  • The PQ curve's ceiling: 10,000 nits

HDR reference white sits at about 2 times the 100 nit SDR level before any highlight headroom is added. In HDR, speculars like sun glints and lamp bulbs use the headroom above that white. That's the part a 1000 nit panel shows and a 400 nit panel has to squeeze.

Brightness in a lit room

Room light raises the black of every screen, and that cuts into contrast. Take a screen with a 250 nit white and a 0.25 nit black. In a dark room that's 1000:1. If glare off the glass adds 0.5 nits, the black becomes 0.75 nits and contrast falls to 333:1. A screen that makes true black gets 500:1 under the same glare.

So a bright room favors two things: a brighter white, which lifts the picture above the glare, and a screen surface that reflects less. On OLED, brightness has a cost, because running bright and static adds to wear.

Reading a spec sheet

Three questions get you most of the way:

  • Which number is it: typical, peak or sustained? Only typical tells you how SDR use will look.
  • Where was it measured? A small patch and a full white screen give very different numbers.
  • Is there a test behind it? A DisplayHDR tier fixes the method, so a tier number can be compared with another tier number. A bare claim of HDR can't.
Work it out yourselfOpen the HDR Test

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Related terms

HDR (High Dynamic Range)HDR shows a wider span from deep shadows to bright highlights than standard video can. On a monitor the label alone says little, because the result depends on how bright the screen gets, how dark it gets and how much color it covers.OLEDOLED (organic light-emitting diode) screens make light in every pixel, so there's no backlight. A pixel that's off is truly black, which gives very high contrast, but the organic material wears with use and big bright images are held back by a power limit.Mini LEDMini LED is an LCD backlight made of thousands of tiny LEDs grouped into zones that dim on their own. It gives an LCD deeper blacks and brighter highlights than a plain backlight, but a zone is far bigger than a pixel, so a halo can show around bright objects on dark backgrounds.IPS panelIPS (in-plane switching) is an LCD panel type where the liquid crystals turn in the plane of the glass. It keeps color and brightness steady from wide angles, but its native contrast is modest next to VA and OLED, so blacks look dark gray in a dark room.

Sources

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