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If two mobile devices being compared have exactly the same LCD/LED screen (matrix) size and exactly the same battery, will the one with higher resolution have higher battery consumption and thus will require to be charged more often?

For example -- two Kiano tablets:

  • Kiano Core 10.1, 10 inches, 8000 mAh, 800x1200 resolution,

  • Kiano Core 9.7, 10 inches, 8000 mAh, 1536x2048 resolution.

Two devices, the same screen size and battery, resolution nearly twice . Which one should consume battery faster (in any), if both are used in the same way?

Which assumption is more correct:

  1. Second device will consume battery faster, because it has much more pixels to power.

  2. Battery consumption in case of both devices will be quite similar. Second has much more pixels, but since overall screen are a is the same, they're much smaller and therfore will use less energy to power.

I'm a beginner and layman (if not -- ignorant) in this area, so I'm much more convinced to the first assumption. But then, the fact that hardware producer decided to equip both devices with the same battery, though different resolution, that would support second assumption.

Forgive me for asking in a wrong place (if so). But it is really hard to determine, where questions about mobile devices hardware should be asked on Stack Exchange network. I've seen this, this and this -- non of the answer says, where to ask such question. Both SuperUser and this site FAQ and both says that a question asked in an incorrect place, if it covers: "electronic devices, media players, cell phones or smart phones, except insofar as they interface with your computer". Bot non if these two sites expains, where such questions should be asked.

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  • \$\begingroup\$ This is a good and valid question, more on topic here than any other stack. \$\endgroup\$ – Passerby Aug 1 '13 at 22:15
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I expect the high-resolution display to use slightly more, but roughly the same amount of power as the lower-resolution display.

Most of the power consumed by the display in a tablet like this goes to two primary components: the backlight and the LCD.

Typically the backlight consumes very roughly 75% of the energy going to the screen. Most tablets like this one have a CCFL tube backlight; some of them have a "white LED" backlight. It doesn't change the answer for this question -- given either kind of backlight, that backlight will consume exactly the same amount of power no matter what LCD is placed in front of it. Turning the "brightness" down can save a significant amount of energy.

As you probably already know, the "liquid crystal display" (LCD) such as the ones in the tablets you mention act as shutters -- they either let the light through, or they block the light, or something in-between. They typically consume the other 25% or so of the energy going to the screen.

Some of that energy goes to keeping the liquid crystals "open" (or "closed"). A cluster of 4 pixels requires exactly the same power to keep the liquid crystals "open" (or to keep "closed") as a single pixel 4 times the size.

Some of that energy is lost due to parasitic capacitance of the INO transparent "wires" on the screen. The total row capacitance and the total column capacitance is about the same for the two screens, so the amount of energy required to update a row (charging and discharging every column line across the entire screen) is the same. However, the higher-resolution screen has more rows to update, so assuming the same full-screen update rate, it requires more power.

As a side effect of the screen having a higher resultion, the CPU and the CPU-to-display bus will have to do a little more work dealing with more pixels.

So the things that use up the most power use exactly the same amount of power no matter what the resolution. There are a few things that require more energy for the higher-resolution screen. So I expect the high-resolution display to use slightly more, but roughly the same amount of power as the lower-resolution display.

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Power consumption is a function of many factors, besides resolution. So, I don't think your question is answerable, in the general case.

However, I think it's fair to say that most of the power of an LCD screen goes into the backlight. So as a first order approximation, screens of similar size will have similar power requirements.

But also consider other factors: a higher resolution screen will have more spaces between pixels, and thus, may have less area that's transparent to light, thus making the backlight less effective. Yet, a higher resolution screen is likely to be newer, or more expensive, and may utilize different technologies that improve the backlight efficiency or effectiveness.

Also, especially among phones, many of the screens are transflective. Meaning, they are a compromise between a transmissive display, illuminated by a backlight (works well in low ambient lighting) and reflective, illuminated by ambient lighting (works well in the sun). A screen can't be good at both. A very reflective display can turn the backlight off in the sun, but in low light will need a much brighter backlight because the display isn't as transmissive. A very transmissive display won't need much backlighting in low ambient light, but in the sun will have to crank up the backlight to overpower the sun. So, when comparing two displays, the conditions under which they are compared matter.

Also, a display isn't of much use unless it has something to display. It's a reasonable guess that a higher resolution display is paired with a more capable graphics processor. It may be that this additional processing power comes at the cost of higher electrical power. Or, the higher resolution phone may be newer, or cost more, and thus be able to process graphics more efficiently. Or, it could be that a manufacturer included a higher resolution screen as a marketing gimmick and actually didn't beef up the graphics processing to effectively use the additional resolution in all cases. It's anyone's guess.

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  • \$\begingroup\$ +1. However, I don't know about "newer, or cost more, and thus be able to process graphics more efficiently." Is that an appeal to novelty, or am I committing the "appeal to tradition" fallacy? \$\endgroup\$ – davidcary Aug 2 '13 at 3:00
  • \$\begingroup\$ @davidcary for all kinds of processors, GPUs included, performance per watt goes up with time, and with more money, one can also afford a newer, more advanced processor, delivering more performance per watt. \$\endgroup\$ – Phil Frost Aug 2 '13 at 11:07
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Think about how much light is needed to come from each display per square centimetre or square inch - this of course is a vast generalism but if the higher resolution screen (the same size) pumped the same power into each pixel it'd be a lot brighter. Does it need to be brighter? Maybe, if folk have complained that the lower resolution screen is dim!

I suspect that the higher resolution screen need only consume the same power as the lower reso screen because it is bright enough.

There is of course small print - more pixels needs more column/row drivers and these aren't 100% efficient so maybe there is a tad more power in the higher reso screen OR maybe they have boosted the efficiency of the LEDs a tad.

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protected by Kortuk Jan 30 '14 at 14:51

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