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ExtLume
What it is
ExtLume is a Windows tray app for adjusting external monitor brightness when Windows provides a brightness slider only for a laptop panel. It offers a separate slider for each safely identified active external display and shows its EDID model name. When the monitor and full cable or dock connection support DDC/CI, ExtLume adjusts the physical backlight. If hardware control is unavailable, it can apply a click-through software overlay to a safely isolated external desktop area; this dims the image but does not reduce backlight power.
The app 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 public beta is available from GitHub Releases as a per-user installer or portable ZIP. It works offline and requires no administrator rights. Its controls are limited to brightness; it does not provide input switching, profiles, scheduling, CLI, or API access.
For and against
For
- Separate slider for each safely identified active external display
- Supports DDC/CI backlight control
- Handles mirrored groups, hot-plugging, and resume
- Works offline and requires no administrator rights
- Installer and portable ZIP options
Against
- Brightness control only; no input switching or profiles
- No scheduling, CLI, or API access
- Software dimming does not reduce backlight power
- Public releases are beta builds
The verdict
ExtLume focuses on external monitor brightness, with DDC/CI control and a software overlay fallback. Its Windows-only beta and brightness-only feature set are important limits to consider.
Who it suits
ExtLume suits Windows users who want separate brightness control for external monitors, especially when their display and connection support DDC/CI. Its software dimming option may help when hardware control is unavailable, provided the external desktop area is safely isolated.
Plans and prices
ExtLume
Public beta builds · Windows 10 and Windows 11 · per-user installer or portable ZIP
Read 7 Oct 2026 · github.com
On the record
- 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 · read 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 · read 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 · read 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 · read 7 Oct 2026
- License and status
- The repository identifies ExtLume as MIT-licensed and says current public releases are beta builds.github.com · read 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 · read 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 · read 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 · read 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 · read 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 · read 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 · read 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 · read 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 · read 7 Oct 2026
