Real-Time Brightness Adjustment When Charging (macOS)

This solution automatically sets your macOS display brightness to 100% when the power adapter is connected. It leverages a LaunchDaemon that runs a persistent script listening for power state changes via pmset. This event-driven approach ensures immediate response without unnecessary polling.

Requirements

macOS (tested on recent versions)
brightness CLI (install directly from GitHub, see below)
Administrative privileges

1. Install the `brightness` CLI

Important: Do NOT install via Homebrew. The Homebrew package is outdated and broken.

Instead, install from GitHub:

git clone https://github.com/nriley/brightness.git
cd brightness
make
sudo cp brightness /usr/local/bin/

2. Create the Power Monitoring Script

This script continuously monitors power events and sets brightness to 100% when AC power is detected.

Open an editor to create the script:

sudo nano /usr/local/bin/brightness-monitor.sh

Paste the following content,

#!/bin/bash

# Absolute path to the brightness command
BRIGHTNESS_CMD="/usr/local/bin/brightness"

# Monitor power events in real time using pmset
pmset -g pslog | while read -r line; do
    if echo "$line" | grep -q "AC Power"; then
        echo "AC Power detected. Setting brightness to 100%."
        $BRIGHTNESS_CMD 1
    fi
done

Save and exit (Ctrl + X, then Y, then Enter).

Make the script executable,

sudo chmod +x /usr/local/bin/brightness-monitor.sh

3. Create the LaunchDaemon

This LaunchDaemon runs the monitoring script at boot and keeps it alive.

Open an editor to create the daemon configuration,

sudo nano /Library/LaunchDaemons/com.user.brightness-monitor.plist

Insert the following XML content:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
    <dict>
        <key>Label</key>
        <string>com.user.brightness-monitor</string>
        <key>ProgramArguments</key>
        <array>
            <string>/usr/local/bin/brightness-monitor.sh</string>
        </array>
        <key>RunAtLoad</key>
        <true/>
        <key>KeepAlive</key>
        <true/>
    </dict>
</plist>

Save and exit.

4. Load the LaunchDaemon

Set proper permissions and load the daemon,

sudo chmod 644 /Library/LaunchDaemons/com.user.brightness-monitor.plist
sudo chown root:wheel /Library/LaunchDaemons/com.user.brightness-monitor.plist
sudo launchctl unload /Library/LaunchDaemons/com.user.brightness-monitor.plist 2>/dev/null
sudo launchctl load /Library/LaunchDaemons/com.user.brightness-monitor.plist

Verification & Troubleshooting

Manual Test
Run the script manually to confirm functionality:

sudo /usr/local/bin/brightness-monitor.sh

You should see a message indicating that AC power was detected and brightness is being set to 100%.

Logs
If the daemon does not trigger as expected, inspect system logs for hints:

log show --predicate 'process == "launchd"' --last 5m | grep brightness

How It Works

The script runs continuously in the background.
It listens for power events using pmset -g pslog.
Upon detecting "AC Power", it invokes the brightness command (via its absolute path) to set the display brightness to 100%.
The LaunchDaemon ensures the script is started at boot and remains running.

Happy coding and enjoy your automatically optimized brightness!

coltenkrauter/auto-brightness-plugged-in-macos.md