Advanced Configuration and Power Interface Specification

ACPI-Defined Devices and Device-Specific Objects
Arguments:
None
Return Value:
An Integer containing the ambient light temperature in degrees Kelvin
0 – The current reading is below the supported range or sensitivity of
Ones (-1) –
Other values –
the sensor
The current reading is above the supported range or sensitivity of
the sensor
9.2.5 _ALR (Ambient Light Response)
The current ambient light color chromaticity x and y coordinate
values, per the CIE Yxy color model
This object evaluates to a package of ambient light illuminance to display luminance mappings that
can be used by an OS to calibrate its ambient light policy for a given sensor configuration. The OS
can use this information to extrapolate an ALS response curve - noting that these values may be
treated differently depending on the OS implementation but should be used in some form to calibrate
ALS policy.
Arguments:
None
Return Value:
A variable-length Package containing a list of luminance mapping Packages. Each mapping
package consists of two Integers.
The return data is specified as a package of packages, where each tuple (inner package) consists of
the pair of Integer values of the form:
{, }
Package elements should be listed in monotonically increasing order based upon the ambient light
illuminance value (the Y-coordinate on the graph) to simplify parsing by the OS.
Ambient light illuminance values are specified in lux (lumens per square meter). Display luminance
(or brightness) adjustment values are specified using relative percentages in order simplify the
means by which these adjustments are applied in lieu of changes to the user’s display brightness
preference. A value of 100 is used to indicate no (0%) display brightness adjustment given the lack
of signed data types in ACPI. Values less than 100 indicate a negative adjustment (dimming); values
greater than 100 indicate a positive adjustment (brightening). For example, a display brightness
adjustment value of 75 would be interpreted as a -25% adjustment, and a value of 110 as a +10%
adjustment.
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