Brightness
After this page you will know whether the brightness feature can work on your Mac, and why it is off by default.
Last updated 22 August 2026
macOS sends the brightness keys to one display, and it is not always the one you are looking at. On a Mac with several displays that is a small daily irritation.
Brightness keys control the display under the pointer changes where those keystrokes go.
What it needs
The app intercepts the keys with an event tap, and an event tap needs accessibility permission. Without it there is nothing to intercept and the feature simply stays off.
The app never prompts for that permission from the interception code. It asks in Settings, where you asked for the feature, because a permission prompt that arrives out of nowhere is a permission prompt people deny.
| What Settings shows | What it means |
|---|---|
| The switch is on and nothing is said | The tap is live |
| The brightness keys could not be intercepted on this Mac | The tap could not be created even though the app is trusted |
| The switch is on but nothing happens | Accessibility permission has not been granted |
What it can actually change
Two mechanisms, and which one applies depends on the display.
A physical monitor with a DDC channel. The app talks to the monitor over DDC and changes the panel’s own backlight. This is real brightness, and it is what you want.
Everything else. There is a gamma-based fallback, which changes what is sent to the display rather than what the display does with it.
A virtual display has no DDC channel, because there is no panel behind it. Brightness on a virtual display is therefore the gamma path or nothing.
| Capability | macOS | State | Why |
|---|---|---|---|
| Physical monitor over DDC | 14.0 and later | Available | Changes the panel's own backlight, if the monitor implements DDC. |
| Built-in Mac display | 14.0 and later | Partial | macOS owns it. The keys work; this feature only decides which display they reach. |
| Virtual display | any | Unavailable | No DDC channel, because there is no panel. Gamma is the only lever, where it works. |
| Gamma fallback | 26.3 and later | Unavailable | Reports success and changes nothing visible on some Apple silicon. Detected at launch and disabled. |
Settings, General
- Open at login
- On
- Show group name in the menu bar
- On
- Confirm before switching groups
- Off
- Allow virtual displays
- On
- Save arrangement changes automatically
- Off
- Brightness keys control the display under the pointer
- Off The brightness keys could not be intercepted on this Mac.
Sliders on the display itself
The brightness keys are one half. The other half is in the group window: select a display that is live right now and its card ends in a Hardware Controls section.
What appears there is decided by the display, not by the app. Each display is probed once when you select it, and a control that the panel does not answer for is absent rather than present and dead. At most you get three:
| Control | VCP | Present when |
|---|---|---|
| Brightness | 0x10 | The panel answers for luminance |
| Contrast | 0x12 | The panel answers for contrast |
| Volume | 0x62 | The panel answers for speaker volume |
A display that answers for none of them says so in one line, which is the useful answer: it tells you the monitor is not reachable over DDC/CI rather than leaving you to wonder whether the app is broken.
Brightness is the one control that is shown even when it cannot move, because it is the one people go looking for. Where neither the panel nor the gamma path can change anything, the slider is present, disabled, and says why.
Why it is off by default
It needs accessibility permission, it intercepts a system key, and on plenty of machines it can do nothing useful. A feature with all three of those properties should be something you turn on deliberately, not something that asks for a permission on first launch.
What this is not
MoreDisplays is not a monitor control utility. What is here is what a group needed anyway: the keys landing on the right display, and sliders for the controls a panel answers for. There is no input switching, no power control, no per-app dimming and no colour work. If driving monitors over DDC is the problem you are solving, there are apps built entirely around it and they will serve you better.
Next
- Remote clients for what your client does with the display.
- Troubleshooting when a setting refuses to turn on.