Brightness Sync is a free, open-source macOS menu-bar utility that keeps one or more LG UltraFine displays locked in step with your MacBook's built-in screen brightness — so a single keystroke or ambient-light adjustment fans out to every panel simultaneously.
What is Brightness Sync?
Brightness Sync is a lightweight macOS utility that mirrors your MacBook's internal display brightness to connected LG UltraFine monitors in real time. Because Apple's own brightness controls treat the UltraFine as a separate island, you'd normally reach for the monitor's own keys whenever you move from a sun-flooded desk to a dim evening setup — Brightness Sync eliminates that friction entirely.
The app lives quietly in your menu bar, wakes only when brightness changes, and otherwise consumes virtually no CPU or memory. It's the kind of tool you install once and then forget exists — which is exactly what a good utility should do.
What does Brightness Sync do best?
Its single responsibility — keeping monitor brightness in perfect ratio with the built-in display — is executed without compromise. The moment macOS raises or lowers the MacBook panel (whether you hit a key, let True Tone respond to the room, or trigger Night Shift), Brightness Sync catches that event and pushes the equivalent value to every UltraFine on the chain.
I run a MacBook Pro paired with two 27-inch LG UltraFines. Before Brightness Sync, coming back to the desk after a meeting meant squinting at a whiteboard-bright external while the laptop had auto-dimmed. Now all three panels dim and brighten as one. The synchronisation feels instantaneous — I've never caught a lag between the internal and external updates.
The app also handles multi-monitor setups gracefully. Both UltraFines track the same brightness curve, which matters more than it sounds: mismatched panels on a wide desk are genuinely tiring over a long session.
Is Brightness Sync free?
Yes — Brightness Sync is completely free to download and use, with no paid tier, no subscription, and no in-app prompts. The source code is publicly available on GitHub under an open-source licence, so the community can audit, fork, and contribute freely. If you want to thank the developer, the repository page is the place to look.
Who should use Brightness Sync?
Anyone who pairs a MacBook with one or more LG UltraFine displays and finds the manual brightness mismatch annoying. That's a surprisingly large audience: the UltraFine line was co-designed with Apple and remains one of the few third-party monitors that can charge a MacBook over USB-C and respond to macOS brightness commands at all — but Apple's own sync logic stops at a single level of consistency that leaves multi-display owners wanting.
If you work across changing light conditions — a home office with shifting natural light, a studio, or a café setup where you dock and undock frequently — Brightness Sync will earn its keep within the first hour. If your UltraFine sits in a fixed, controlled environment where you never touch brightness, the utility is still harmless but arguably unnecessary.
It's worth noting that Brightness Sync is purpose-built for LG UltraFine hardware. It won't do anything useful for a Dell, BenQ, or Samsung display — for those you'd look at tools like MonitorControl, which uses DDC/CI to address a wider range of panels. Brightness Sync trades breadth for perfect depth on its target hardware.
How does Brightness Sync compare to MonitorControl?
MonitorControl is the more versatile option — it targets any DDC/CI-capable display and adds volume control, contrast, and fine-grained per-input settings. If you own a mixed monitor setup or something other than an LG UltraFine, MonitorControl is the right pick. But on a UltraFine specifically, Brightness Sync's dedicated integration feels more responsive and requires zero configuration: there are no display profiles to set up, no DDC command timeouts to wait through. I've run both; for a pure UltraFine rig, Brightness Sync wins on simplicity and reliability.
What are the best Brightness Sync alternatives?
For LG UltraFine owners, there isn't a direct like-for-like alternative — Brightness Sync is the only purpose-built sync tool for this hardware family. The closest substitutes are:
- MonitorControl — broader DDC/CI support; slightly more setup friction on UltraFines.
- Lunar — a full-featured (and partly paid) display manager with adaptive brightness, hotkeys, and app-based rules. Powerful but heavier.
- BetterDisplay — tackles resolution scaling and EDR alongside brightness; overkill if you only want sync.
For straightforward brightness synchronisation on a UltraFine, none of these rivals the elegance of a tool that does exactly one thing.
