Gloam

The free, open-source, all-in-one monitor control and eye protection tool for Windows: brightness, dimmer and blue-light filter in one tiny tray app.

Gloam is a free and open-source Windows tray utility, written in AutoHotkey v2, that puts everything you need to control your screens and protect your eyes in one place:

• Hardware brightness over DDC/CI: changes the monitor's real backlight, just like the buttons on the monitor.
• Software dimmer and blue-light filter via the GPU gamma ramp: no overlay window, so screenshots, fullscreen apps and games are unaffected.
• Scenes (Reading / Office / Movie / Night) and an automatic day/night schedule that fades smoothly between two scenes.

Left-click the tray icon (or press Win+Alt+B) to open a compact dark control panel in the bottom-right corner of the screen.

Features

• Hardware brightness slider and quick presets (25 / 50 / 75 / 100 %) for the primary monitor
• Software dimmer (1-100 %) and blue-light filter (0-100 %)
• Per-monitor dimmer settings, or apply to All Monitors at once
• Four built-in scenes, all editable at the top of the script
• Auto schedule with a gradual fade (default: 07:00 day, 20:00 night, 60 min transition)
• Optional "wider dimming range" to dim down to 1 % instead of Windows' default 50 % floor
• Settings remembered between runs
• Handles monitors being plugged in/out, and re-applies the gamma ramp if sleep, unlock or another app resets it
• Original gamma is restored when the script exits

Requirements

• Windows 10 or 11
• AutoHotkey v2.0 (the script uses #Requires AutoHotkey v2.0)
• For hardware brightness: a monitor with DDC/CI enabled (see Troubleshooting). The dimmer and blue-light filter work without it.

Installation

1. Install AutoHotkey v2.
2. Download Gloam.ahk or Gloam.exe from this repository Releases.
3. Double-click it. A tray icon appears and the script is running.

To start it with Windows, put a shortcut to the script in your Startup folder (Win+R, type shell:startup, press Enter).

Usage

Hotkeys

Hotkey	Action
Win+Alt+B	Show / hide the control panel
Win+Alt+Up / Win+Alt+Down	Hardware brightness +10 % / -10 % (primary monitor)
Win+Alt+Right / Win+Alt+Left	Software dimmer +5 % / -5 % (selected monitor(s))
Win+Alt+X	Turn the dimmer on / off
Win+Alt+F1	Scene: Reading
Win+Alt+F2	Scene: Office
Win+Alt+F3	Scene: Movie
Win+Alt+F4	Scene: Night

Control panel

• Monitor selector: choose which monitor the dimmer and blue-light sliders affect, or "All Monitors".
• Brightness (monitor): hardware brightness via DDC/CI, with 25 / 50 / 75 / 100 % preset buttons.
• Dimmer: software dimming through the gamma ramp.
• Blue light filter: reduces the green and blue channels for a warmer picture.
• Scene buttons: Reading, Office, Movie, Night.

The panel closes when it loses focus, when you press Esc, or when you click the red ✕.

Tray menu

• Brightness Control: open the panel (this is also the single-click action)
• Dimmer enabled: toggle the dimmer
• Auto schedule (day/night): fade automatically between the day and night scenes
• Wider dimming range (admin + restart): see below
• Exit: restores the original gamma and quits

Scenes

Each scene is [dimmer %, blue-light filter %]:

Scene	Dimmer	Blue-light filter
Reading	75 %	35 %
Office	90 %	10 %
Movie	60 %	25 %
Night	30 %	60 %

Scenes apply to the monitor(s) currently selected in the panel. Note that the Night scene's 30 % dimmer needs the wider dimming range (see below); otherwise it is clamped to 50 %.

Auto schedule

When enabled from the tray menu, the script blends from DAY_SCENE to NIGHT_SCENE and back over the configured transition time, checking every 30 seconds. Defaults:

Setting	Default
Day starts	07:00
Night starts	20:00
Fade length	60 minutes
Day scene	Office
Night scene	Night

Manual tweaks stick between fades: the schedule only overwrites your values while the fade is actually moving.

Wider dimming range

By default Windows rejects gamma ramps darker than about 50 %, so the dimmer cannot go below that. The tray option Wider dimming range (admin + restart) sets the registry value

HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\ICM
    GdiIcmGammaRange = 256 (DWORD)

which unlocks dimming down to 1 %. It needs administrator rights (the script asks via UAC) and a Windows restart, after which you start the script again. Choosing the option again removes the value and returns to the default range.

Configuration

Edit the settings block at the top of Gloam.ahk:

STEP        := 10                  ; hardware hotkey step (%)
DIM_STEP    := 5                   ; dimmer hotkey step (%)
PRESETS     := [25, 50, 75, 100]   ; hardware preset buttons (%)
THROTTLE_MS := 40                  ; min delay between DDC/CI writes while dragging

SCENES := Map("Reading", [75, 35]
            , "Office",  [90, 10]
            , "Movie",   [60, 25]
            , "Night",   [30, 60])

DAY_START   := 7  * 60             ; minutes after midnight
NIGHT_START := 20 * 60
TRANSITION  := 60                  ; length of the fade, in minutes
DAY_SCENE   := "Office"
NIGHT_SCENE := "Night"

Your dimmer values, blue-light values and auto-schedule state are saved to an .ini file next to the script (same name, .ini extension) when the panel closes and when the script exits.

How it works

• Hardware brightness uses the Windows dxva2 monitor configuration API (SetMonitorBrightness, with a fallback to VCP feature 0x10) to talk to the monitor over DDC/CI. Writes are throttled so dragging the slider doesn't flood the display bus.
• Software dimming scales the red, green and blue channels of each display's gamma ramp with SetDeviceGammaRamp. The blue-light filter lowers green by up to 28 % and blue by up to 62 %. If Windows rejects a ramp as too dark, the script backs off step by step until one is accepted.
• The gamma ramp is re-applied every 5 seconds, because sleep, unlock and some other apps can reset it.

Limitations

• Hardware brightness controls the primary monitor only. The dimmer and blue-light filter work on every monitor.
• Other programs that also change the gamma ramp (colour calibration tools, other blue-light or night-mode utilities) will compete with this script, so run only one at a time.
• Because the dimmer works through the gamma ramp, it reduces the output levels of your display; it does not change backlight strength.
• Windows only.

Troubleshooting

"Failed to initialize monitor" / hardware slider shows N/A

1. Enable DDC/CI in the monitor's on-screen display (OSD) menu.
2. Unplug and replug the monitor's cable.
3. Update your graphics drivers.

Some connections (certain docks, adapters and KVM switches) and most built-in laptop panels don't support DDC/CI. In that case the dimmer and blue-light filter still work.

The dimmer won't go below 50 %: enable the wider dimming range described above.

Colours look wrong after the script crashed: restart the script and exit it from the tray menu, which restores the default gamma ramp. Signing out or restarting Windows also resets it.

License

Gloam is free and open source.