Advanced Configuration and Power Interface Specification

ACPI-Defined Devices and Device-Specific Objects
that approaches a fully-bright display (100% absolute) in very bright ambient environments
regardless of the user’s display brightness preference. Using a small value for max (e.g. 0% @ 300
lux) would influence the ALS policy to limit the use of this technology solely as a power-saving
feature (never brighten the display). Conversely, setting min to a 0% adjustment instructs ALS
policy to brighten but never dim.
A minimum of two data points are required in the return package, interpreted as min and max. Note
that the baseline value does not have to be explicitly stated; it can be derived from the response
curve. Addition elements can be provided to fine-tune the response between these points. Figure 9-
52 illustrates the use of two data points to achieve a response similar to (but simpler than) that
described in Figure 9-51 .
Min
Baseline
Max
Amb ie n t L ig h t Illu mi n an ce ( Lu x)
1200
350
90
20
5
(70,30)
Dimly-Lit
Conference
Room
Typical
Office
Brightly-Lit
Café
(150,1000)
0
(70,0)
-30% -20% -10% 0% +10% ...
Display Luminance (Brightness) Adjustment
Figure 9-52 A two-point ALS Response Curve
+50%
This example lacks an explicit baseline and includes a min with an ambient light value above 0 lux.
The baseline can easily be extrapolated by ALS Policy (e.g. 0% adjustment at ~400 lux). All
ambient light brightness settings below min (20 lux) would be treated in a similar fashion by ALS
policy (e.g. -30% adjustment). This two-point response curve would be modeled as:
Name(_ALR, Package() {
Package{70, 30}, // Min ( -30% adjust at 30 lux)
Package{150,1000} // Max ( +50% adjust at 1000 lux)
})
This model can be used to convey a wide range of ambient light to display brightness responses. For
example, a transflective display – a technology where illumination of the display can be achieved by
reflecting available ambient light, but also augmented in dimly-lit environments with a backlight –
could be modeled as illustrated in Figure 9-53.
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