Battery life and screen background?

[Guest]

Archived from groups: alt.sys.pc-clone.dell (More info?)

Does anyone here know if using a black background on a laptop will
improve the battery life, because the LCD won't be displaying anything
for the background? Is "black" like "off"? If 25% of the background
is showing, would using a black background be like keeping 25% of the
screen off? Or doesn't it work that way?

Thanks.

-Joel

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[Guest]

Archived from groups: alt.sys.pc-clone.dell (More info?)

joel@exc.com (Dr. Joel M. Hoffman) wrote in
news:aSHZe.13503$H24.11396@fe11.lga:

> Does anyone here know if using a black background on a laptop will
> improve the battery life, because the LCD won't be displaying anything
> for the background? Is "black" like "off"? If 25% of the background
> is showing, would using a black background be like keeping 25% of the
> screen off? Or doesn't it work that way?


Actually, black is "on" in a LCD. An LCD works by powering up the pixels
to block the white light that either comes from the backlight or is
passively reflected.

University of Illinois at Champaign actually did a study of this once on
an IBM Thinkpad laptop with a 14.1" LCD display. LCD power consumption
(not counting backlight) was 1.01 Watts with a black background; 0.93
Watts with a white background; and 0.99 Watts with the default windows
background.

But this difference of 0.08 Watts pales in comparison to the backlight
itself, which is typically in the 3 to 30 watt range depending on exact
tehnology used - Desktop LCD monitors typically used flourescent
backlights that use 20-30 watts (or more); Laptop LCDs typically use
electroluminescent backlights that use 3-5 watts.


- FM -

see also:

http://www.crhc.uiuc.edu/
~mahesri/classes/project_report_cs497yyz.pdf#search='lcd%20backlight%
20power%20consumption'