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SPECIFICTION
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ExtLume

github.com

Free plan Windows
Visit github.com
Spec score 7.4 #15 of 24 in Monitor Control Software

What it is

ExtLume is a Windows tray app for adjusting external-monitor brightness when Windows provides a brightness control only for the laptop panel. It offers a separate slider for each safely identified active external display and shows its EDID model name. When the monitor and the full cable or dock chain support DDC/CI, the app changes the physical backlight. If that is unavailable, it can use a click-through dimming overlay on a safely isolated external desktop area; this changes the image but 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 Windows 11 and requires .NET Framework 4.8. The free, MIT-licensed public beta is available from GitHub Releases as a per-user installer or portable ZIP and requires no administrator rights. ExtLume says it works offline without telemetry or network requests. It stores limited local monitor and dimming data, and its controls are limited to brightness rather than arbitrary VCP commands, resets, or automatic display substitution.

Spec sheet

Purpose
ExtLume is a Windows tray app for adjusting external monitor brightness when Windows provides a brightness slider only for the laptop panel.Read 7 Oct 2026 · github.com
Privacy
ExtLume says it works offline with no telemetry, analytics, crash upload, update check, account, cloud synchronization, advertising identifier, or network request.Read 7 Oct 2026 · github.com
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.Read 7 Oct 2026 · github.com
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.Read 7 Oct 2026 · github.com
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.Read 7 Oct 2026 · github.com
Display handling
It handles multiple displays, mirrored display groups, hot-plugging, and resume, and excludes built-in panels and virtual displays from control.Read 7 Oct 2026 · github.com
Hardware mode
It controls physical monitor backlight through DDC/CI when the monitor and complete cable or dock chain support it.Read 7 Oct 2026 · github.com
License and status
The repository identifies ExtLume as MIT-licensed and says current public releases are beta builds.Read 7 Oct 2026 · github.com
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.Read 7 Oct 2026 · github.com
Monitor controls
The app provides a separate slider for each safely identified active external display and shows its EDID model name.Read 7 Oct 2026 · github.com
Permissions
The installer uses the current user's profile and does not request elevation; the app requires no administrator rights.Read 7 Oct 2026 · github.com
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.Read 7 Oct 2026 · github.com
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.Read 7 Oct 2026 · github.com

Plans and prices

ExtLume Free Public beta builds · Windows 10 and Windows 11 · per-user installer or portable ZIP Read 7 Oct 2026 · github.com

Every ExtLume plan and price →

Strong points and limits

Strong points

  • Separate brightness slider for each identified external display.
  • DDC/CI controls physical backlight when supported.
  • Free, MIT-licensed public beta.
  • Portable ZIP or per-user installer; no admin rights.
  • Works offline without telemetry or network requests.

Limits

  • Requires Windows 10 or 11 and .NET Framework 4.8.
  • Software dimming does not reduce backlight power.
  • No input switching, profiles, or scheduled settings.
  • Duplicate-mode dimming is blocked in a specified shared-display case.

Who it suits

It suits Windows laptop users who need brightness control for external monitors. Users whose monitor or complete connection path lacks DDC/CI can use software dimming where the external desktop area is safely isolated.

Verdict

ExtLume focuses on external-monitor brightness, with hardware control when the monitor and connection support DDC/CI and a limited software fallback. Its Windows-only scope and beta status are worth weighing, as are its brightness-only controls.

Where Specifiction places it

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