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Do brighter colours save LCD power?
dreamlayers:
Do LCDs use more power to display dark pixels? Pixels are normally transparent, and a voltage needs to be applied to make them less transparent. This presumably uses some power. I remember reading about tests of PC monitor power consumption, which found LCD monitors use more power when displaying a black screen.
Update: Measurements taken via FS#9728 and FireWire input power show that on my 5th generation 30 GB iPod, a white screen uses about 2 mA less than a black screen.
Chronon:
Interesting, since I have been led to believe there shouldn't be any current flow in a TFT display element (not that I expected no power to be consumed, of course). Is consumption higher while switching -- e.g. for a flickering screen? I suppose that will take extra work to test. . .
soap:
I don't know if this tool is sharp enough to see the (I assume) teeny tiny difference we are talking about, or if repeated carefully controlled runtime tests will be needed.
dreamlayers:
--- Quote from: Chronon on January 28, 2009, 08:10:59 PM ---Interesting, since I have been led to believe there shouldn't be any current flow in a TFT display element (not that I expected no power to be consumed, of course).
--- End quote ---
LCD elements are driven by AC (because DC would degrade the LCD via electrochemical changes). Each element has some capacitance, making it like a capacitor connected to AC when darkened, and using power. There may be a some very slight leakage current also.
--- Quote from: Chronon on January 28, 2009, 08:10:59 PM ---Is consumption higher while switching -- e.g. for a flickering screen? I suppose that will take extra work to test. . .
--- End quote ---
I know that would use power because new data needs to be generated and sent to the display. I don't think the display elements themselves would use more power because they must be refreshed constantly anyways.
--- Quote from: soap on January 28, 2009, 08:27:55 PM ---I don't know if this tool is sharp enough to see the (I assume) teeny tiny difference we are talking about, or if repeated carefully controlled runtime tests will be needed.
--- End quote ---
I have seen repeatable results both with FS#9728 and by measuring FireWire current with a multimeter.
Here's a study of this on PC monitors. (I'm linking to an archived page because the site seems down.)
Chronon:
--- Quote from: dreamlayers on January 28, 2009, 09:38:57 PM ---LCD elements are driven by AC (because DC would degrade the LCD via electrochemical changes). Each element has some capacitance, making it like a capacitor connected to AC when darkened, and using power. There may be a some very slight leakage current also.
--- End quote ---
I was not aware of that. I think you mean electromechanical, but I take your point.
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