Backlight power consumption analysis.

[Colin Ian King]

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