Advanced Configuration and Power Interface Specification

Advanced Configuration and Power Interface Specification
Min
Baseline
Max
Amb ie n t L ig h t Illu mi n an ce ( Lu x)
1200
350
90
20
5
(73,10)
(85,80)
Dimly-Lit
Conference
Room
(100,300)
Typical
Office
Brightly-Lit
Café
(150,1000)
0
(70,0)
-30% -20% -10% 0% +10% ...
Display Luminance (Brightness) Adjustment
+50%
Figure 9-51 A five-point ALS Response Curve
Figure 9-51 illustrates the use of five points to approximate an example response curve, where the
dotted line represents an approximation of the desired response (solid curve). Extrapolation of the
values between these points is OS-specific – although for the purposes of this example we’ll assume
a piecewise linear approximation. The ALS response curve (_ALR) would be specified as follows:
Name(_ALR, Package() {
Package{70, 0}, // Min ( -30% adjust at 0 lux)
Package{73, 10}, // ( -27% adjust at 10 lux)
Package{85, 80}, // ( -15% adjust at 80 lux)
Package{100,300}, // Baseline ( 0% adjust at 300 lux)
Package{150,1000} // Max ( +50% adjust at 1000 lux)
})
Within this data set exist three points of particular interest: baseline, min, and max. The baseline
value represents an ambient light illuminance value (in lux) for the environment where this system is
most likely to be used. When the system is operating in this ambient environment the ALS policy
will apply no (0%) adjustment to the default display brightness setting. For example, given a system
with a 300 lux baseline, operating in a typical office ambient environment (~300 lux), configured
with a default display brightness setting of 50% (e.g. 60 nits), the ALS policy would apply no
backlight adjustment, resulting in an absolute display brightness setting of 60 nits.
Min and max are used to indicate cutoff points in order to prevent an over-zealous response by the
ALS policy and to influence the policy’s mode of operation. For example, the min and max points
from the figure above would be specified as (70,0) and (150,1000) respectively – where min
indicates a maximum negative adjustment of 30% and max represents a maximum positive
adjustment of 50%. Using a large display brightness adjustment for max allows an ALS response
502 April, 2015 Version 6.0