Checklist of brightness control guidelines for system manufacturers

System manufacturers should follow the guidelines that are described in this section when they develop Windows 8 platforms with integrated displays.

Basic display control functionality

The display miniport driver must expose the display brightness control functionality by implementing the WDDM DXGK_BRIGHTNESS_INTERFACE_2 interface. The presence of this interface indicates that the driver supports brightness control of the integrated display (see Brightness control platform infrastructure).
The driver must set bit 2 of the argument to the _DOS ACPI control method. With the setting of bit 2, the system basic input/output system (BIOS) is informed that it should not perform any automatic brightness changes.
The system must adhere to all System.Client.BrightnessControls requirements in the Windows Hardware Certification Requirements.

Ensure that brightness can be modified through the main user interfaces, namely the sliders in the Settings charm, the Power Options page, and the Windows Mobility Center.
Ensure that AC/DC transitions result in brightness changes as defined by the AC/DC display brightness levels.
Ensure that the display dims after the period of user inactivity specified in the dim display after setting.
Validate that the system meets all the System.Client.BrightnessControls requirements and passes all the corresponding tests.

The system must implement brightness up and down hot keys using Human Interface Device (HID) usages (preferred) or ACPI (see Brightness control platform infrastructure).
If HID implementation is chosen, the auto-repeat functionality should not be implemented by the system manufacturer. This functionality is implemented by Windows.
If ACPI implementation is chosen, the embedded controller must implement auto-repeat. The first repeated notification should be sent approximately 500 ms after a button is pressed and held. The repeat rate should be such that there is a total end-to-end delay of approximately 2.5 seconds to reach from 0 to 100 (or vice versa).

Ensure that every brightness up (or down) hot key button press results in a 10% brightness policy increase (or decrease), and a corresponding change in display brightness.
Ensure that auto-repeat works. The total end-to-end delay must to be approximately 2.5 seconds.

The display miniport driver must implement it as part of fully implementing the WDDM DXGK_BRIGHTNESS_INTERFACE_2 interface.
The platform hardware and display miniport driver must support scenario-based backlight optimization on the internal display panel even when external display(s) are attached.
The display miniport driver must support user-initiated brightness changes even when the scenario-based backlight optimization is enabled.
The display miniport driver must support scenario-based backlight optimization both when ALS-based adaptive brightness is enabled and disabled.
The system must adhere to all System.Client.BrightnessControls.BacklightOptimization requirements in the Windows Hardware Certification Requirements.

Validate that scenario-based backlight optimization works during single display and attached display scenarios.
Ensure that user changes to brightness through the UI or hot keys work correctly when scenario-based backlight optimization is enabled.
Ensure that scenario-based backlight operation works correctly both when ALS-based adaptive brightness is enabled and disabled.
Validate that the system meets all the System.Client.BrightnessControls.BacklightOptimization requirements and passes all the corresponding tests.

The display miniport driver must implement the WDDM DXGK_BRIGHTNESS_INTERFACE_2 interface and indicate support for smooth brightness control using the capability bit defined in that interface.
The driver must report 101 levels to Windows. Brightness is reported as a percentage, so this covers the range between 0 and 100, inclusive.
Smooth brightness control in the driver must be implemented without depending on the embedded controller.
Smooth brightness transitions must complete in less than 500 ms.
The Windows Display Driver Model (WDDM) driver must continue to support smooth brightness control even when scenario-based backlight optimization is in effect.
Connecting additional display devices to the system must not impact the ability to perform smooth transition on the integrated panel.
Adhere to all System.Client.BrightnessControls.SmoothBrightness requirements in the Windows Hardware Certification Requirements.

Validate that brightness changes due to UI, hot keys, display dimming, and ALS occur smoothly.
Validate that brightness can be set to each of the reported 101 levels.
Ensure that smooth brightness changes do not rely on the embedded controller.
Validate that each smooth brightness transition completes in less than 500 ms.
Validate that brightness transitions remain smooth even when scenario-based backlight optimization is in effect.
Ensure that the display brightness on the main panel changes smoothly even when an additional display is connected to the system.
Validate that the system meets all the System.Client.BrightnessControls.SmoothBrightness requirements and passes all the corresponding tests.

Configure the settings labeled "Should" in Table 1 Settings and customization requirements in Guidelines for brightness control policy configuration.
If perceived as improving the balance between user experience and power optimization, configure the settings labeled as "May" in Table 1 Settings and customization requirements in Guidelines for brightness control policy configuration.
Do not change the default values for any of the settings labeled as "No" in Table 1 Settings and customization requirements in Guidelines for brightness control policy configuration.