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Old 12-12-2011, 08:03 PM
Colin Ian King
 
Default Backlight power consumption analysis.

Hi there,

More power consumption analysis... this time I investigated the current
drawn when cycling through all the back-light levels on various
machines. The results are interesting as they show non-linearity in
power consumption. A brief summary of my findings is:


All machines showed up non-linear current increase as backlight levels
increasse.

At the highest backlight setting the machines show a reduction of battery
life from ~12-22%. The Lenovo ThinkPad X220i shows a remarkable increase in
power consumption as we approach the highest brightness levels, and so does
the HPMini-100 to a lesser degree.

The general rule of thumb therefore is try not to exceed more than 2/3 the
way up the brightness scale. The top 1/3 of the brightness scale impacts
of power consumption disproportionately.

If you want to see the data and some interesting graphs, I've put a
LibreOffice spreadsheet in

with a brief write-up of the results in:

http://zinc.canonical.com/~cking/power-benchmarking/backlight-non-linearity/

Colin

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Old 12-13-2011, 08:01 AM
John Johansen
 
Default Backlight power consumption analysis.

On 12/12/2011 01:03 PM, Colin Ian King wrote:
> Hi there,
>
> More power consumption analysis... this time I investigated the current drawn when cycling through all the back-light levels on various machines. The results are interesting as they show non-linearity in power consumption. A brief summary of my findings is:
>
> All machines showed up non-linear current increase as backlight levels increasse.
> At the highest backlight setting the machines show a reduction of battery
> life from ~12-22%. The Lenovo ThinkPad X220i shows a remarkable increase in
> power consumption as we approach the highest brightness levels, and so does
> the HPMini-100 to a lesser degree.
>
> The general rule of thumb therefore is try not to exceed more than 2/3 the
> way up the brightness scale. The top 1/3 of the brightness scale impacts
> of power consumption disproportionately.
>
This matches with what I would expect, LEDs efficacy suffers as you increase
the current. This is known as droop and it is what sets the limit of a LED's
brightness.

> If you want to see the data and some interesting graphs, I've put a LibreOffice spreadsheet in
> with a brief write-up of the results in:
>
> http://zinc.canonical.com/~cking/power-benchmarking/backlight-non-linearity/
>
So out of curiosity did you test with the back light off to get a measure of
what the draw was for just turning it on?

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Old 12-13-2011, 08:20 AM
Colin Ian King
 
Default Backlight power consumption analysis.

On 13/12/11 09:01, John Johansen wrote:

On 12/12/2011 01:03 PM, Colin Ian King wrote:

Hi there,

More power consumption analysis... this time I investigated the current drawn when cycling through all the back-light levels on various machines. The results are interesting as they show non-linearity in power consumption. A brief summary of my findings is:

All machines showed up non-linear current increase as backlight levels increasse.
At the highest backlight setting the machines show a reduction of battery
life from ~12-22%. The Lenovo ThinkPad X220i shows a remarkable increase in
power consumption as we approach the highest brightness levels, and so does
the HPMini-100 to a lesser degree.

The general rule of thumb therefore is try not to exceed more than 2/3 the
way up the brightness scale. The top 1/3 of the brightness scale impacts
of power consumption disproportionately.


This matches with what I would expect, LEDs efficacy suffers as you increase
the current. This is known as droop and it is what sets the limit of a LED's
brightness.


If you want to see the data and some interesting graphs, I've put a LibreOffice spreadsheet in
with a brief write-up of the results in:

http://zinc.canonical.com/~cking/power-benchmarking/backlight-non-linearity/


So out of curiosity did you test with the back light off to get a measure of
what the draw was for just turning it on?

Not yet ;-)

Colin

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