Why does BetterDisplay show a different brightness percentage than my monitor?

BetterDisplay’s brightness percentage may describe software dimming or a combined brightness scale rather than the monitor’s hardware setting. The two percentages describe different scales. Neither directly measures emitted light in nits.

With Combined brightness enabled, one slider can span hardware brightness, software dimming below the hardware minimum, and supported XDR/HDR upscaling. The switchover point and other range settings determine how the slider uses these methods. A combined value of 50% may correspond to a different percentage on the monitor.

If you want the main slider to use hardware brightness alone when available, open Settings > Displays > [display] > Device Control and turn off Combined brightness. You need a working hardware-brightness controller. For DDC brightness, both the monitor and connection must support DDC.

Software dimming changes the displayed image without changing the monitor’s brightness number. Returning software brightness to its neutral level removes that dimming, so the image can become brighter while the monitor’s own number remains unchanged. If software brightness is set to full black, raise software brightness to make the image visible again.

If the monitor uses a hardware range such as 0–50, BetterDisplay needs that range to convert its percentage correctly. Open Device Control > DDC Control > Configure Controls…, select brightness, and check DDC value range minimum and DDC value range maximum. Set the range supported by your monitor if detection reported it incorrectly. Do not assume every model uses 0–100. If the level resets after sleep, see reapplying DDC settings on wake.

On a Sidecar iPad, BetterDisplay’s dimming changes the displayed image. It does not adjust the iPad’s own brightness setting. Use the iPad’s Control Center when you want to change that setting. Any power savings depend on the iPad’s panel and displayed content, rather than the app’s percentage alone.

If you want software dimming without DDC changes to the monitor, open Settings > Displays > [display] > Device Control > Add or Remove Controllers… and remove DDC Control. You can still use software Image Adjustments. Removing DDC also stops its other hardware commands, such as input or volume control. Settings already stored by the monitor remain in place. Other configured hardware controllers also remain enabled.

If you specifically selected hardware control and the monitor’s own setting still does not follow, investigate DDC communication and readback separately. Some monitors accept writes but do not provide reliable readings. See Image Adjustments and DDC control.

A monitor preset can lock hardware brightness even while DDC successfully reads its current value. If the hardware slider moves and then returns to the old value, check the monitor’s own picture preset, low-blue-light mode and HDR settings. If brightness is locked there too, switch to a preset that permits adjustment and try again. Which modes impose this restriction depends on the monitor. Changing BetterDisplay’s percentage range will not unlock a level fixed by the monitor.