GNOME developer Sebastian Wick has announced that when GNOME 49 ships on September 17, 2025, it will include a major rework of how the desktop environment handles screen brightness—especially on HDR displays.
This update builds on changes introduced in GNOME 48 but streamlines the entire system for more consistent control, multi-monitor support, and better HDR performance. Here’s what it’s all about.
HDR is tightly tied to luminance—the raw brightness a display can output—making precise control essential. The issue is, however, that many external HDR monitors simply lock out brightness adjustments through their on-screen menus when HDR mode is enabled.
That’s frustrating, but GNOME’s display compositor, Mutter, has already been using a clever “software backlight” trick to work around it, shifting the white signal level so the display appears dimmer or brighter without touching the physical backlight.
The second big challenge involves “HDR headroom”—the gap between maximum possible luminance and the brightness of reference white. If there’s no HDR content on screen, keeping the backlight maxed out wastes power.
Ideally, brightness should be adjusted dynamically in sync with what’s being shown. Unfortunately, the existing sysfs backlight API isn’t well-suited for this, so Wick says GNOME is preparing to use a new Kernel Mode Setting (KMS) backlight API.
This centralized system now supports multiple displays, multiple backlights per display, and input from various sources—like quick settings, keyboard shortcuts, power-saving dimming, and ambient light sensors.
The Quick Settings menu has also been updated, letting users adjust brightness on individual screens and removing the old “HDR Brightness” slider from GNOME Settings. So, according to Wick, once the new KMS backlight API lands upstream, GNOME will be ready to plug it in and start dynamically tuning HDR headroom in real time.
For more information, see Wick’s blog post.
