There are three tiers, each determined by the maximum brightness. DisplayHDR 400 is aimed more at laptops, where power and size tend to limit what's possible. A monitor meeting this spec has to reach a brightness of 400 nits, offer true 8-bit color (at 95 percent of the BT.709 gamut), provide global display dimming and support the HDR10 format. That may not sound like much, but it's 50 percent brighter than typical laptops, many of which 'cheat' to get 8-bit color through dithering. DisplayHDR 600 ramps up the brightness to 600 nits while requiring improved black levels and 99 percent BT.709 color accuracy (plus 90 percent of DCI-P3). The most advanced monitors can aim for DisplayHDR 1000, which supplies at least 1,000 nits and even deeper blacks.
The spec is limited to LCD monitors for now, although there are hopes to adapt it to OLED displays and other technology. And you won't have to wait long to see it in use -- VESA is promising DisplayHDR-rated products at CES in January. This doesn't guarantee that you'll be blown away by a Netflix movie or an HDR-enabled game, but it should discourage companies from pulling a fast one by slapping an HDR label on a display that doesn't do the technology justice. Also, it could improve the adoption of HDR among your preferred hardware makers. If they know what to shoot for, they may be more likely to add HDR support instead of holding back out of uncertainty.