ExtLume
ExtLume is a Windows tray app for adjusting external monitor brightness when Windows offers a brightness slider only for the laptop panel.
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 provides 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, ExtLume controls the physical backlight. If that is unavailable, it can use a click-through software dimming overlay on a safely isolated external desktop area; this changes the displayed image, not backlight power. The app handles multiple displays, mirrored groups, hot-plugging, and resume, and excludes built-in and virtual displays. It 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. It needs no administrator rights and says it works offline without telemetry, analytics, crash uploads, update checks, accounts, cloud sync, advertising identifiers, or network requests. ExtLume is MIT licensed, and its current public releases are beta builds. Its controls are limited to brightness; it does not offer input switching, profiles, scheduling, CLI, or API access.
Good
- Separate control for each identified external display
- Can control backlight through DDC/CI
- Software dimming fallback when safely isolated
- Handles multiple displays and hot-plugging
- Offline operation and no administrator rights
Watch out
- Current public releases are beta builds
- Software overlay does not reduce backlight power
- Brightness control only; no profiles or scheduling
- Requires .NET Framework 4.8
Who it suits
ExtLume suits Windows 10 or 11 users who need brightness controls for external displays. It is most relevant when the monitor and its connection support DDC/CI or when software dimming can be safely isolated.
Verdict
ExtLume focuses on external-display brightness, with hardware control where the monitor and complete connection support DDC/CI. Its fallback has a different effect, and the app deliberately excludes some display configurations to avoid dimming a built-in panel.
Plans and prices
From ExtLume's own pricing page, checked 7 Oct 2026.
| Plan | Price | What it gives you |
|---|---|---|
| ExtLume | Free | Public beta builds · Windows 10 and Windows 11 · per-user installer or portable ZIP |
The facts
Each one read from ExtLume's own pages, with the date it was checked.
What it does
- 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.checked 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.checked 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.checked 7 Oct 2026
- Hardware mode
- It controls physical monitor backlight through DDC/CI when the monitor and complete cable or dock chain support it.checked 7 Oct 2026
- License and status
- The repository identifies ExtLume as MIT-licensed and says current public releases are beta builds.checked 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.checked 7 Oct 2026
- Monitor controls
- The app provides a separate slider for each safely identified active external display and shows its EDID model name.checked 7 Oct 2026
- Permissions
- The installer uses the current user's profile and does not request elevation; the app requires no administrator rights.checked 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.checked 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.checked 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.checked 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.checked 7 Oct 2026
Where it runs
- 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.checked 7 Oct 2026
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