brisyncd - macOS display brightness synchronization daemon

This daemon (user agent) can be used to synchronize the brightness of an external display with a main (integrated) display. This is especially useful if the brightness of your main display is automatically controlled by an ambient light sensor (Macbook Pro, for example).

brisyncd receives notifications from the system about displays connection/disconnection and automatically selects display to get the brightness from and displays to apply the brightness to.

Installation

Using brew

brew install aleksey-mashanov/brisyncd/brisyncd
brew services start brisyncd

Manual

swift build -c release
cp `swift build -c release --show-bin-path`/brisyncd /usr/local/sbin/
cp io.github.aleksey-mashanov.brisyncd.plist ~/Library/LaunchAgents/
launchctl load ~/Library/LaunchAgents/io.github.aleksey-mashanov.brisyncd.plist

Configuration

To make all your displays look alike in the full range of the main display brightness tuning of the transfer function is required. This can be done using four parameters: min, max, gamma and contrast.

brisyncd reads configuration from ~/.brisyncd.json and /usr/local/etc/brisyncd.json (the first found of them, can be overridden using --config command-line option). Configuration file is a JSON with the following structure (all fields are optional, comments here are for readability, they must be omitted in the config file):

{
    "source": "Color LCD",  # name of the source display
    "min": 0,               # default minimum brightness level (default: 0)
    "max": 100,             # default maximum brightness level (default: 100)
    "gamma": 1.0,           # default brightness gamma correction (default: 1.0)
    "contrast": null,       # default contrast (default: null)
    "interval": 50,         # default update interval, ms. (default: 50)
    "targets": {            # dictionary of targets with custom configuration
        "DELL U2720Q": {    # keys of the dict are names of the target displays
            "min": 35,      # minimum brightness level
            "max": 85,      # maximum brightness level
            "gamma": 2.2,   # brightness gamma correction
            "contrast": 75, # normal contrast
            "interval": 50  # update interval, ms.
        }
    },
    "targetsOnly": true     # manage known targets only (default: false)
}

See /usr/local/sbin/brisyncd help config for more information.

The simplest way to create custom configuration is to dump a configuration detected by brisyncd to a file and then modify it:

/usr/local/sbin/brisyncd config -o ~/.brisyncd.json

brisyncd reads configuration file on startup so don't forget to restart it after modification:

brew services restart brisyncd

Why brisyncd

• brisyncd receives notifications from the system when the main display brightness changes.
• Brightness is synchronized in real-time, with no visible delays.
• There are no timers, no background and periodic jobs which can consume the battery.
• brisyncd just does its job - no UI, no keyboard shortcuts, no additional features.
• brisyncd does not use AppleLMUController so it is compatible with the latest MacBook Pro.
• Can be tuned for displays with different peak brightness and brightness function.
• Can use contrast to darken display beyond 0% brightness.
• Supports heterogenous multi-display configurations.

Displays supported

brisyncd uses DDC/CI to control display brightness so it works for displays which support this specification.

Docking stations are known to not support DDC/CI proxying.