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Color affects the additional energy consumption of a GUI in
several ways. Our first experiment measures the energy of iPAQ1
when the CPU is idle for one second with screens of different
colors. Since each pixel consists of three color components, R, G,
and B, we perform measurement for colors containing different
combinations of these three components. We also perform
measurements with the LCD turned off to obtain the energy
consumption of the LCD only. Table VII summarizes the
results under energy consumed by the LCD and the non-LCD energy.
It also shows the percentage energy increase compared with pure
white. R, G, B, and RG refer to red, green, blue, and orange,
respectively. They have R, G, B, and R and G component(s)
deactivated, respectively. ``Grey" refers to the color obtained
when the corresponding originally activated component(s) is (are)
half-activated. For example, when all three components are fully
activated, the color is ``Full" black. When they are
half-activated, the color is ``Grey" black.
Table VII:
Energy breakdown for presenting screens of different
colors
Color |
Non-LCD (EU) |
LCD (EU) |
% Increase |
Black |
Full |
36,100 |
18,700 |
3.3 |
|
Grey |
36,100 |
19,100 |
5.5 |
Red |
Full |
36,100 |
18,500 |
2.2 |
|
Grey |
36,100 |
18,700 |
3.3 |
Green |
Full |
36,100 |
18,500 |
2.2 |
|
Grey |
36,100 |
18,700 |
3.3 |
Blue |
Full |
36,100 |
18,600 |
2.8 |
|
Grey |
36,100 |
18,700 |
3.3 |
RG |
36,100 |
18,300 |
1.1 |
White |
36,100 |
18,100 |
0 |
The energy difference disappears after the LCD is turned off,
which demonstrates that it is the LCD that makes the difference.
There are two observations one can make. First, the more color
components activated, the more the energy consumption. In a
reflective TFT LCD, when one color component is deactivated, the
corresponding liquid crystals are fully unpolarized, and there is
no need to repeatedly charge the polarizers. For instance,
``White" has all three color components deactivated and consumes
the least energy, while ``Black" has all three activated and
consumes more energy. This observation is the same as that made
in [3] for a transmissive TFT LCD. More
interestingly, the second observation is that a half-activated
component consumes more energy than an activated component, as the
``Grey" ones consume more energy than their ``Full" counterparts.
As mentioned in Section III, each color component has
a TFT to charge a storage capacitor, which maintains the
appropriate voltage between the polarizers. When a component is
half-activated, the capacitor puts the TFT into a state that draws
a higher amount of current, which contributes to higher energy
consumption.
On Zaurus, users can choose different colors for GUI themes.
Table VIII gives the system energy for presenting
the ``Application" window with different colors for the QPE theme
for one second. It confirms the observation made in the iPAQ1
experiment. It also shows the percentage system energy increase
when compared with that of the ``Bright" theme color.
Table VIII:
Energy of different colors for the QPE theme on
Zaurus
Theme color |
Energy (Joule) |
Over Bright(%) |
Bright |
0.416 |
0 |
Purple |
0.417 |
0.4 |
Desert |
0.422 |
1.5 |
Grey |
0.423 |
1.6 |
Next: Color sequence
Up: Window properties
Previous: Size
Lin Zhong
2003-10-13