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Swirnoff
2010-08-06, 23:57
Does the display use up less energy with darker themes?

DrWilken
2010-08-07, 00:05
It should *cost* less to display black (completely black).

Swirnoff
2010-08-07, 00:07
By any appreciable amount?

Wikiwide
2010-08-07, 00:07
Maybe. Theoretically, it should, but such factors as brightness of screen, applications used, keyboard back-light are also influencing the energy usage. You will have to experiment a lot to prove that black theme and wallpaper use less energy than white theme and white wallpaper.

DrWilken
2010-08-07, 00:11
Did a quick Google search on the topic and found this -> http://www.digitalsignageblog.com/2009/03/02/does-black-pixels-on-an-lcd-screen-use-less-power-than-white/

Guess I might be wrong:

There are two modes of LCDs, normally white and normally black. This means that, at rest, not powering the transistor, the window (sub-pixel of the LCD) is either open or closed. LCDs were once all “normally white” since a display is usually more white than black (look at your PC monitor). Normally white will use less power if more of the display is white or a light color. This mode was picked years ago so notebooks would use less power. The problem arose when the notebook industry, followed by the monitor industry, and finally the TV industry found that dead transistors meant that the little sub-pixel window is “open” all the time. This is the cause of the dreaded stuck bright red, green or blue dot.
The answer is that all large area LCDs are normally black. Normally blacks use more power on a typical image (if there is any such thing as a typical image), than normally white displays. So, today’s set use more power but the dead pixels are black and not stuck on. A fair compromise in my opinion.
DB


Found this too -> http://blogs.msdn.com/b/dthorpe/archive/2007/08/03/black-pixels-cost-less.aspx


While it's true that a black pixels consumes less power than a white pixels on a CRT screen, pixel color has no effect on LCD power consumption. Given that LCDs are a large and growing (and possibly majority) portion of the global monitor population, the power savings claimed by blackle.com is a case of diminishing returns.

DrWilken
2010-08-07, 00:20
As Wikiwide says, turn down the brightness.

Install Simple Brightness Applet if You haven't already (or just change it in Settings - Display).

I'm only using 2 (of 5) bars and it's enough for me.... ;)

Benson
2010-08-07, 00:31
As mentioned above, CRTs see (some) power saving when more pixels are black. Same goes for plasma and OLED screens.

Some LCDs (typically TVs and some computer monitors) do have local backlight control, such that they can dim the backlight in a dark region of the screen -- while this is targeted mainly at enhanced dynamic range, it also saves some power, but it's per-sector, not per-pixel, so it's not clear how much difference a white-on-black vs. black-on-white theme would make.

Most LCDs, including the ones in the N900, have a single backlight controlled by a single brightness control, which directly affects power draw. While the display matrix power consumption may be better with white or black pixels, the total display matrix power is significantly less than the backlight power, so IMO this isn't worth worrying about at all -- better to pick a theme that maximizes readability so you can dial the brightness down a notch.

DrWilken
2010-08-07, 00:35
... Or buy a big set of glasses... :)

http://s3.images.com/huge.40.200310.JPG

shadowjk
2010-08-07, 13:15
The "power saving" setting in display settings makes the backlight dim if there's alot of black onscreen, and other way around with white.. So even if white takes less power on the LCD, the backlight is working harder.. ;-)

Kangal
2010-08-07, 14:47
I read a paper when they did Google in black-dominant rather than white-dominant pages. It turned out black uses more power than white, disproving the initial hypothesis.

I read not too long ago on XDA-devs, that red uses the least.

Perhaps the colour that uses the least is dependant on the screens (or screen types I should say) that you're testing.
Or perhaps red uses even less than black and Google didn't experiment this with the same study.

edit: found it it's http://www.blackle.com/

MOC
2010-08-07, 15:14
As Wikiwide says, turn down the brightness.

Install Simple Brightness Applet if You haven't already (or just change it in Settings - Display).

I'm only using 2 (of 5) bars and it's enough for me.... ;)

I second that and would like to add that turning down the brightness can make reading a lot more comfortable on a pc too.

quingu
2010-08-07, 22:18
My own findings after intensive testing with a thinkpad notebook are that a completely white LCD consumes measurably less power than a completely black screen.
Measurable, but far from being significant. If at all, it would result in maybe <5mins difference in runtime, with the screen running all the time. Any actual cpu work would have a far bigger impact.

If you really want to save power that way, choose a high-contrast theme that allows viewing the screen with lower backlight.

fraz
2010-08-09, 00:45
My own findings after intensive testing with a thinkpad notebook are that a completely white LCD consumes measurably less power than a completely black screen.
Measurable, but far from being significant. If at all, it would result in maybe <5mins difference in runtime, with the screen running all the time. Any actual cpu work would have a far bigger impact.

If you really want to save power that way, choose a high-contrast theme that allows viewing the screen with lower backlight.

I would agree. Since to make black, an LCD has a backlight then applies current to all the LCD pixels to block the backlight and produce black, (rather than their usual transparent state)

It does get rather complicated though when you consider some LCDs automatically dim the back light when showing dark images to artificially increase their contrast ratio. And others are black when no voltage is applied to the pixels, and go clear when voltage is applied (eg VA LCDs). Seems like the N900 doesn't fall into one of these catagories though.

So basic advice would be use a high contrast theme so you can turn down your backlight which uses most of the LCDs power anyway. :)