Buying guide
HDR brightness windows, local dimming, and what specs omit
How to read HDR brightness claims on gaming monitors, why window size and picture mode change the numbers, how Mini LED local dimming compares with OLED, and what spec sheets leave out.
“1,300 nits peak” on a spec sheet rarely tells you how bright a monitor looks in your game. HDR brightness depends on how much of the screen is bright, which picture mode you use, and how the monitor manages power and heat.
Nits and window sizes
Brightness is measured in nits (candelas per square meter). Testers measure a white patch covering a percentage of the screen, called the window:
- 1% to 3% windows represent small highlights: a sun, a muzzle flash, a lamp.
- 10% windows are a common middle ground.
- 25% windows approach bright scenes.
- 100% (full screen) represents a bright sky or a white document.
OLEDs reach their highest numbers only in small windows, then dim as more of the screen is bright. This is automatic brightness limiting (ABL). For example, TFTCentral measured about 1,800 nits for a 1% window on the ASUS PG27AQWP-W in its brightest HDR mode, while its SDR Uniform Brightness mode holds about 381 nits. Both numbers are correct; they describe different situations.
Picture modes change the result
Many OLEDs offer a “Peak 1000” style mode and a “True Black 400” or “True Black 500” mode. Peak modes chase high highlight brightness; True Black modes track the HDR standard more accurately at lower peaks. TFTCentral measured about 1,000 nits in the PG32UCDM3's Gaming and Cinema modes and about 530 nits in its True Black 500 mode. Always check which mode a measurement used.
VESA DisplayHDR tiers
VESA certifies monitors at tiers such as DisplayHDR 400, 600, and 1000 for LCDs, and True Black 400 and 500 for OLEDs. The number roughly indicates peak brightness requirements, and True Black tiers add strict black-level requirements. DisplayHDR 400 on an LCD without local dimming delivers little real HDR contrast.
Mini LED local dimming vs OLED
A Mini LED backlight splits the backlight into hundreds or thousands of zones that dim independently. The AOC U27G4XM has 1,152 zones; Tom's Hardware measured over 1,100 nits and about 13,000:1 HDR contrast with local dimming on Medium. Mini LED is excellent for bright, full-screen HDR, but zones are much larger than pixels, so small bright objects on dark backgrounds can show halos (blooming).
OLED controls every pixel, so it has no blooming and perfect blacks, but lower full-screen brightness. Which looks better depends on the content and your room.
What spec sheets leave out
- The window size and mode behind the peak brightness claim.
- How long brightness is sustained before dimming.
- Whether local dimming works in the accurate color modes. Tom's Hardware found it locked out of the sRGB and P3 modes on the BenQ EX321UX.
- Firmware changes that alter HDR behavior after launch.
- How the coating handles room light, which changes perceived contrast more than a few extra nits.
When comparing HDR monitors, use measurements from the same outlet, at the same window size, in comparable modes.