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
(0,1000)
Brightly-Lit
Café
Typical
Office
Dimly-Lit
Conference
Room
(200,30)
0
(70,0)
(180,0)
0% +40% +80% +100%
Display Luminance (Brightness) Adjustment
Figure 9-53 Example Response Curve for a Transflective Display
This three-point approximation would result in an ALS response that allows the backlight to increase
as the ambient lighting decreases. In this example, no backlight adjustment is needed in bright
environments (1000+ lux), maximum backlight may be needed in dim environments (~30 lux), but a
lower backlight setting may be used in a very-dark room (~0 lux) – resulting in an elbow around 30
lux. This response would be modeled in _ALR as follows:
Name(_ALR, Package() {
Package{180, 0} ( +80% adjust at 0 lux)
Package{200, 30}, // Max (+100% adjust at 30 lux)
Package{0, 1000}, // Min ( 0% adjust at 1,000 lux)
})
Note the ordering of package elements: monotonically increasing from the lowest ambient light
value (0 lux) to the highest ambient light value (1000 lux).
The transflective display example also highlights the need for non-zero values for the user’s display
brightness preference – which we’ll refer to as the reference display brightness value. This
requirement is derived from the model’s use of relative adjustments. For example, applying any
adjustment to a 0% reference display brightness value always results in a 0% absolute display
brightness setting. Likewise, using a very small reference display brightness (e.g. 5%) results in a
muted response (e.g. +30% of 5% = 6.5% absolute). The solution is to apply a reasonably large
value (e.g. 50%) as the reference display brightness setting – even in the case where no backlight is
applied. This allows relative adjustments to be applied in a meaningful fashion while conveying to
the user that the display is still usable (via reflected light) under typical ambient conditions.
504 April, 2015 Version 6.0