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ow ALS Works
To understand how ALS works, you first need to understand the following terms:
Lux — A measurement of light. Average indoor lighting ranges from 70 to 300 lux. A cloudy day outdoors measures
around 5000 lux. A sunny day outdoors could measure as much as 10,000 lux.
Nit — A unit of measurement of screen brightness. Depending on the type of LCD, the maximum brightness can
range from 150 to 220 nits. Most of Dell's LCD panels have a maximum brightness of around 180 nits and a
minimum brightness of 10 nits. The higher the nits, the brighter the display. ALS is capable of adjusting the LCD
brightness smoothly over the full panel brightness range.
EEDID Step — Enhanced Extended Display Identification Data Step. This data set is stored on each LCD panel and
contains information for eight predefined panel brightness steps. BIOS or the QuickSet brightness control (not ALS)
uses this step information to adjust the panel brightness. These eight incremental steps typically encompass the
range of nits from 10 to 220 (or whatever the maximum brightness of the display). For example, it may use the
following settings: 10, 17, 24, 30, 60, 110, 150, 220.
SMBus — System Management Bus. The computer uses this communication method to access the EEDID steps
and to control the brightness through the BIOS or shortcut keys.
The following table shows approximately how the ALS adjusts based on certain conditions.
The ALS sensor measures the amount of ambient light in the area and passes this information to the M07 inverter chip. A
calculation is made to determine how bright the display needs to be within the settings (minimum and maximum) based on
the light in the environment. The panel brightness is then automatically adjusted to the calculated level to compensate. This
is done continually to allow the display to adapt to the environment. The brighter the light in the area, the brighter the screen
gets; the darker the ambient light, the darker the display.
The brightness adjustment process occurs over several seconds, so you do not see a sudden shift from bright to dark or
vice versa. Also, depending on the settings made to the minimum/maximum slider under the ALS controls, you may see no
adjustment at all, as the appropriate setting may fall outside of the threshold set.
Since ALS can adjust the screen smoothly over the full brightness range as opposed to the eight predefined steps, it
provides you with more brightness flexibility than previously available. You must tweak the ALS settings to suit personal
preferences.
DPST
Display Power Savings Technology (DPST) analyzes the display image data and, based on the results, may reduce the
panel brightness up to 30 percent. The analysis and resulting brightness adjustment are intended to be undetectable. This
technology was developed by Intel and is only available on systems that have the Intel GMA 950 Integrated Controller. The
range of brightness adjustment is from 0 to 30 percent and is only enabled when the system is running on battery power.
This feature is disabled when an external display device is connected.
You can access the DPST settings either through the Intel Graphics control that is part of the Intel video driver or through
QuickSet. These controls are not visible in QuickSet if the system has a discrete video card installed and is not using the
integrated Intel GMA 950 Integrated controller. You can enable or disable the feature, as well as adjust the slider bar for the
aggressiveness of the DPST feature from Max Quality to Max Battery.
NOTE:
These measurements were taken at Dell. User experience will vary, depending on location.
Location
Light Level
(lux)
Typical Panel
Brightness
(nits)
Conference room
(presentation lighting)
70 12
Conference room
(standard lighting)
245 32
Cubical 330 50
Window behind desk
(indirect sunlight)
500 75
Cafeteria
(plentiful sunlight)
765 110
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22/02/2010
https://dcse.dell.com/SelfStudy/Foundations_2007/Foundations_2007_Portables/Portable
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