ExtLume

Free plan Windows

What ExtLume is

ExtLume is a Windows tray app for adjusting external monitor brightness when Windows offers a brightness slider only for the laptop panel. It gives each safely identified active external display its own slider and shows its EDID model name. When the monitor and complete cable or dock chain support DDC/CI, the app controls the physical backlight. Otherwise, it can dim a safely isolated external desktop area with a click-through overlay; this changes the image, not backlight power. ExtLume handles multiple displays, mirrored groups, hot-plugging, and resume, while excluding built-in panels and virtual displays. It targets Windows 10 and 11 and requires .NET Framework 4.8. The free, MIT-licensed beta is available from GitHub Releases as a per-user installer or portable ZIP, and needs no administrator rights. The maker says it works offline without telemetry or network requests. Its controls are limited to brightness; it does not offer input switching, profiles, scheduling, or CLI/API access.

Who it suits

ExtLume suits Windows users who want separate brightness controls for external displays. It may be useful when the monitor supports DDC/CI or when software dimming can be safely isolated from the built-in panel.

What it does well

Separate slider for each safely identified active external display.
Controls physical backlight through supported DDC/CI connections.
Handles mirrored displays, hot-plugging, and resume.
Per-user installer and portable ZIP options.

What to know first

Requires Windows 10 or 11 and .NET Framework 4.8.
Software dimming does not reduce backlight power.
No input switching, monitor profiles, or scheduling.
Public releases are beta builds.

Limits

The app controls brightness only and has no input switching, monitor profiles, scheduling, CLI, or API. Software dimming is unavailable in Duplicate mode when an external display shares its desktop source with the built-in panel and DDC/CI cannot be used.

Plans

Plan	Billed and limits	Price
ExtLume	Public beta builds · Windows 10 and Windows 11 · per-user installer or portable ZIP	Free

As github.com lists them, read 7 Oct 2026. The maker's own page has the final word.

Getting started

Open the ExtLume GitHub repository
Download the per-user installer or portable ZIP from GitHub Releases
Run ExtLume on Windows 10 or Windows 11 with .NET Framework 4.8
Use the separate slider for a safely identified active external display

Verdict

ExtLume focuses on external-display brightness, with hardware control when the full connection supports DDC/CI and a software alternative in some cases. Its brightness-only scope and beta status are worth noting.

Questions

How much does ExtLume cost?

ExtLume is free. The listed plan is free.

Is ExtLume open source?

Yes. The repository identifies it as MIT-licensed.

Which platforms does ExtLume support?

It targets Windows 10 and Windows 11 and requires .NET Framework 4.8.

How can I install ExtLume?

GitHub Releases offers a per-user installer and a portable ZIP. The installer uses the current user’s profile and the app requires no administrator rights.

Does ExtLume have a free trial?

No. It is offered as free software, and no free trial is listed.

Does ExtLume control monitor inputs or profiles?

No. It exposes brightness control only and does not provide input switching or monitor profiles.

Facts from ExtLume's own pages

Compatibility limit: In Duplicate mode, software dimming is blocked when an external display shares its desktop source with the built-in panel and DDC/CI is unavailable, to prevent dimming the built-in display. · github.com, 7 Oct 2026
Control limits: The app exposes brightness control only and does not accept arbitrary VCP codes, perform monitor resets, or silently choose another display if the selected display disappears. · github.com, 7 Oct 2026
Display handling: It handles multiple displays, mirrored display groups, hot-plugging, and resume, and excludes built-in panels and virtual displays from control. · github.com, 7 Oct 2026
Hardware mode: It controls physical monitor backlight through DDC/CI when the monitor and complete cable or dock chain support it. · github.com, 7 Oct 2026
License and status: The repository identifies ExtLume as MIT-licensed and says current public releases are beta builds. · github.com, 7 Oct 2026
Local data: The app may store a SHA-256-derived local monitor identifier and software-dimming percentage, plus its executable path if the user enables Start with Windows; it does not persist raw EDID serial numbers or Windows device paths. · github.com, 7 Oct 2026
Monitor controls: The app provides a separate slider for each safely identified active external display and shows its EDID model name. · github.com, 7 Oct 2026
Permissions: The installer uses the current user's profile and does not request elevation; the app requires no administrator rights. · github.com, 7 Oct 2026
Platform and install: The app targets Windows 10 and Windows 11 with .NET Framework 4.8 and is available as a per-user installer or portable ZIP from GitHub Releases. · github.com, 7 Oct 2026
Privacy: ExtLume says it works offline with no telemetry, analytics, crash upload, update check, account, cloud synchronization, advertising identifier, or network request. · github.com, 7 Oct 2026
Purpose: ExtLume is a Windows tray app for adjusting external monitor brightness when Windows provides a brightness slider only for the laptop panel. · github.com, 7 Oct 2026
Software fallback: When hardware control is unavailable, it can use a click-through software dimming overlay for a safely isolated external desktop area; this does not reduce backlight power. · github.com, 7 Oct 2026
Support: The maker directs users to GitHub Issues for general troubleshooting and recommends including app, Windows, laptop or GPU, monitor, connection path, control mode, and expected-versus-actual result in compatibility reports. · github.com, 7 Oct 2026

Where ExtLume stands on Freedom251

Monitor Control Software#12 of 24