Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
depending on the location of the sensor to the light source. Special values are reserved to indicate out
of range conditions (see below).
Arguments:
None
Return Value:
An Integer containing the ambient light brightness in lux (lumens per square meter)
0 – The current reading is below the supported range or sensitivity of
the sensor
Ones (-1) –
The current reading is above the supported range or sensitivity of
the sensor
Other values –
The current ambient light brightness in lux (lumens per square
meter)
9.2.3 _ALT (Ambient Light Temperature)
This optional control method returns the current ambient light color temperature reading in degrees
Kelvin (°K). Lower color temperatures imply warmer light (emphasis on yellow and red); higher
color temperatures imply a colder light (emphasis on blue). This value can be used to gauge various
properties of the lighting environment – for example, the type of light source. Expected values range
from ~1500°K for candlelight, ~3000°K for a 200-Watt incandescent bulb, and ~5500°K for full
sunlight on a summer day – although readings may vary depending on the location of the sensor to
the light source. Special values are reserved to indicate out of range conditions (see below).
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) –
the sensor
The current reading is above the supported range or sensitivity of
the sensor
Other values –The current ambient light temperature in degrees Kelvin
9.2.4 _ALC (Ambient Light Color Chromaticity)
This optional control method returns the current ambient light color chromaticity readings per the
CIE Yxy color model. The x and y (chromaticity) coordinates are specified using a fixed 10 -4
notation due to the lack of floating point values in ACPI. Valid values are within the range 0
(0x0000) through 1 (0x2710). A single 32-bit integer value is used, where the x coordinate is stored
in the high word and the y coordinate in the low word. For example, the value 0x0C370CDA would
be used to specify the white point for the CIE Standard Illuminant D65 (a standard representation of
average daylight) with x = 0.3127 and y = 0.3290. Special values are reserved to indicate out of
range conditions (see below).
500 April, 2015 Version 6.0