DeckLux

Open ambient-light sensor support for Steam Deck on Windows.

DeckLux is a standalone UMDF 2 driver for the Lite-On LTR-F216A ambient-light sensor used in Steam Deck hardware. It exposes illuminance through the standard Windows sensor APIs with SensorsCx and SPB/I2C. It does not require a companion application, background service, or another handheld project.

Overview

DeckLux 1.1.0 installs both ambient-light sensors on Steam Deck OLED (Galileo) and applies the individual factory calibration stored for each sensor in Valve firmware. Windows sees LTRF as the preferred logical light sensor; its reading is fused from both OLED sensors. LTRS remains available as a nonpreferred raw diagnostic channel. Steam Deck LCD (Jupiter) continues to use its single LTRF sensor.

DeckLux is distributed as a locally test-signed driver. Windows Test Mode must be enabled and Secure Boot must be disabled before it can load. DeckLux requires 64-bit Windows 11 build 22000 or newer.

Download

Download DeckLux 1.1.0 from the GitHub release page. The setup executable automatically selects the correct sensor topology for the detected Steam Deck model. SHA-256 checksums and a portable package are included with the release.

Features

• Standard Windows ambient-light sensor interface through UMDF 2.15 and SensorsCx.
• Direct SPB/I2C access to the LTR-F216A register set.
• Read-only identity probe before the first hardware write.
• 18-bit, 100 ms acquisition at 3x gain.
• Bounded not-ready retries, reset recovery, configuration readback, and suspend/resume lifecycle handling.
• Valve per-device factory calibration read from SMBIOS.
• Occlusion-resistant OLED fusion using a short per-channel median and the brighter fresh channel, with automatic one-sensor fallback.
• Report intervals, thresholds, timestamps, sensor state, and invalid-sample transitions expected by Windows sensor clients.
• Exact-device installation, recorded rollback, live WinRT testing, and focused diagnostics.
• Timestamp-correlated comparison of the preferred fused OLED channel and the secondary raw diagnostic channel.

DeckLux reports illuminance. Windows and individual applications decide how those readings affect display brightness.

Hardware support

Hardware	DeckLux behavior
Steam Deck OLED LTRF	Preferred logical sensor; reports fused OLED lux
Steam Deck OLED LTRS	Installed by default as the raw secondary diagnostic channel
Steam Deck LCD with LTR-F216A	Supported as the single preferred sensor
Steam Deck LCD with TI OPT3001	Not compatible; this is a different sensor
Independently verified LTR-F216A	Supported only through exact-instance opt-in

ACPI\PRP0001 is a generic ACPI identifier, not proof that a device is an LTR-F216A. DeckLux therefore requires an installer-created authorization property on the exact device instance. Applying the INF manually to every matching PRP0001 device does not bypass that check.

The normal installer also requires a Valve Jupiter or Galileo firmware identity. A compatible non-Deck sensor must be independently identified and installed with both its exact instance ID and -AllowCompatibleSensor.

Factory calibration

At 18-bit resolution, 100 ms integration, and 3x gain, DeckLux uses a base conversion of 0.15 lux/count. Valve's firmware calibration constants were defined against the older SteamOS downstream basis of approximately 0.2666667 lux/count, so the installer converts them with the exact ratio:

DeckLux scale = Valve OEM scale * 16 / 9
CalibrationScalePpm = round(DeckLux scale * 1,000,000)

The Valve SMBIOS Type 11 mapping is:

Platform sensor	OEM-string slot	ACPI instance
Jupiter LTRF	2	PRP0001:01
Galileo LTRF	2	PRP0001:00
Galileo LTRS	4	PRP0001:01

The four-byte CalibrationScalePpm device property belongs to one physical sensor; 1,000,000 represents scale 1.0. DeckLux never adds or averages the LTRF and LTRS calibration constants. It calibrates each reading first, then fuses the resulting lux values.

On OLED, each channel has a three-reading temporal window whose individual samples expire after one second; the remaining fresh samples form its median. The preferred channel reports the brighter eligible median. If either sensor is unavailable or stale, it reports the healthy channel; if neither is valid, it reports an invalid sample. This is DeckLux's documented occlusion policy, not a claim to reproduce Valve's unpublished implementation.

The evidence, conversion derivation, property contract, and failure behavior are documented in docs/CALIBRATION.md.

Build

The reproducible release build uses an Enterprise WDK mounted as a drive. Pass its root and the Release configuration to the build script:

.\scripts\build-ewdk.cmd E: Release

The build performs a clean Release x64 compile, runs the core and calibration tests, validates the Universal driver API surface, creates and signs the driver package, compiles the graphical installer, and generates release archives and SHA-256 manifests.

Release artifacts are placed under:

artifacts\release\1.1.0\DeckLux-1.1.0-Setup.exe
artifacts\release\1.1.0\DeckLux-1.1.0-portable.zip
artifacts\release\1.1.0\DeckLux-1.1.0-source.zip
artifacts\release\1.1.0\SHA256SUMS.txt

Validate a built package with:

.\scripts\Test-DeckLuxPackage.ps1 -RequireWdkTools

Install

Read scripts/README.md before enabling Windows Test Mode. It covers Secure Boot, BitLocker precautions, package validation, diagnostics, and rollback.

Run the release installer and approve its Windows UAC prompt:

DeckLux-1.1.0-Setup.exe

The installer verifies the Steam Deck firmware identity and selects its exact topology: ordered LTRF plus LTRS on OLED, or the single LTRF on LCD. It reads each matching factory calibration, validates the package, trusts its exact test certificate, stages the INF, writes device-specific properties, and binds only those instances. The installed payload and rollback state are stored separately:

%ProgramFiles%\DeckLux
%ProgramData%\DeckLux\install-state.json

DeckLux appears in Windows Installed apps after setup. The installer does not alter BCD, Secure Boot, BitLocker, or Test Mode, and never initiates a reboot.

Test live readings

The WinRT test uses the same public API available to Windows applications and does not require Administrator access:

& "$env:ProgramFiles\DeckLux\scripts\Test-DeckLuxSensor.ps1" `
    -DurationSeconds 15 `
    -SampleIntervalMs 500

JSON and CSV output are available for logging:

& "$env:ProgramFiles\DeckLux\scripts\Test-DeckLuxSensor.ps1" -OutputFormat Json
& "$env:ProgramFiles\DeckLux\scripts\Test-DeckLuxSensor.ps1" -OutputFormat Csv

Inspect OLED fusion

On Steam Deck OLED, inspect the preferred fused channel and secondary raw channel in shared sampling cycles:

& "$env:ProgramFiles\DeckLux\scripts\Compare-DeckLuxSensors.ps1" `
    -DurationSeconds 20 `
    -SampleIntervalMs 250

The comparison tool requests fresh readings from both WinRT sensor clients, correlates them by sensor timestamp, and reports pair delta and ratio only when both samples are valid and within the allowed skew. LTRF is labelled PreferredFused; LTRS is labelled SecondaryRaw. The tool temporarily adjusts the clients' report interval, latency, and lux thresholds, then verifies that every changed value was restored. It observes driver output and never changes display brightness or the fusion policy.

Focused diagnostic collection is also available:

& "$env:ProgramFiles\DeckLux\scripts\Collect-DeckLuxDiagnostics.ps1"

Uninstall and rollback

Remove DeckLux from Settings > Apps > Installed apps, or reopen DeckLux.Setup.exe and select Uninstall.

It uses the recorded installation state to restore the exact device to its previous binding, restore or remove only properties owned by DeckLux, delete only the recorded driver package, and remove test certificates only when that installation added them. It does not force package removal, disable Test Mode, or initiate a reboot.

Author and license

DeckLux was created and is maintained by Laszlo Toth lavx@lavx.hu. Author information is also embedded in the source headers, package notice, INF metadata, and binary version resources.

DeckLux is free and open-source software under the Microsoft Public License. When DeckLux source or compiled work is distributed or incorporated into another project, the copyright, license, and attribution notices included with the work must be retained. See AUTHORS.md and NOTICE.md.

Third-party references and implementation provenance are recorded in THIRD_PARTY_NOTICES.md. The GPL-2.0-only Linux LTR-F216A driver was used only as a behavioral reference; DeckLux's Windows implementation is independent and MS-PL licensed.

Independence and trademarks

DeckLux is not affiliated with, sponsored by, or endorsed by Valve Corporation, Microsoft Corporation, or Lite-On Technology Corporation. Steam and Steam Deck are trademarks or registered trademarks of Valve Corporation. Product names are used only to describe compatibility.