5

I was trying to find out if screens with different resolutions have different effects on the battery life. Around the net, I see a common answer as no to the question: "Will changing screen resolution increase my battery life?". It is claimed that the reason is the total number of pixels are still the same on the screen and hence, the same effort is being spent by GPU, etc. From here, this sounds legit to me although I am not sure if this is correct or not.

Nevertheless, my question is: "Will screens with same size, same brightness but with different resolutions affect battery differently?" To me, they will since the number of pixels needed to be worked on will differ but I don't know if this is true or not. So, will they?

In short, would power consuption of two monitors that are exactly the same only with one difference; their PPI, be different?

  • I can't. I don't have two computers conforming these specifications. – Utku Sep 16 '15 at 19:04
6

Between two LCD displays identical aside from the physical PPI (and resolution), the one with the higher PPI (and resolution) will use more power for at least two (related) reasons:

  1. More pixels = more transistors to power
  2. More transistors on the panel = reduced light throughput = more power needed to match the brightness of the other display.

Sending a non-native resolution signal to the monitor may actually increase power usage (of the display) by necessitating the use of a scaler circuit that would otherwise be off, or may decrease it by reduced need of other resources. Note that this does not account for a change in power usage outside of the display (e.g. GPU, which may increase or decrease based on a variety of factors).


The day you chose to ask this question happens to be pretty fantastic. Anandtech just published an article comparing the QHD+ and 1080p display options for the 2015 Razor Blade 14".

It's not perfect, as there are more differences between the displays than the PPI/Resolution and they are counting the entire system power, not just that of the display. But they found 17-22% longer battery life with the 1080p than with the QHD+.

| improve this answer | |
  • I read that the most power is drawn for illuminating the screen on laptops. Since you claim "More transistors on the panel = reduced light throughput = more power needed to match the brightness of the other display.", I think that a higher PPI display will significantly increase the power consumption. Is that correct? – Utku Sep 16 '15 at 20:49
  • @Utku Yep. See my addition. – 8bittree Sep 16 '15 at 22:59
3

No, the resolution of the screen will not affect battery life. The reason for that is that, as you said, the actual number of pixels is the same. The monitor cannot turn pixels on or off, as this would literally cause there to be little black spots visible on the monitor given that the pixel size is hardware based, and cannot be changed on the fly.

UPDATE: If PPI is different but everything else is the same then the number of the pixels on the monitor is different and thus the power consumption will be different (the one with higher PPI will use more power).

The below is a more detailed explanation by analogy, to help give you an idea of how monitors actually work to virtually "scale" pixels. Note that the monitor still uses all available pixels, regardless of what it is displaying.


Zooming in too far

Think of how an image is scaled up or down on a computer screen. When you zoom too far in, it gets blurry, because the size of each pixel in the image begins to take up more than one pixel on the monitor.

To display the image, the monitor's pixel size actually does not change, but rather it begins to use multiple monitor pixels to display a single image pixel.

This means that the image has gained additional density, however the monitor has not gained or lost any density and is still displaying the same number of pixels.

Zooming out too far

To make the issue more clear, try to think about that in reverse. When you scale an image down too far, the monitor's pixels become larger than the the pixels in the image.

Imagine you scale an image down to half its original height and width. For the monitor to properly display the image, each of its pixels must represent four of the image's pixels (two in each direction, making a 2x2 square). The monitor does this by having the pixel display the color calculated by taking the average of the four pixels on the image that it represents.

This means that the image has lost some density, because the monitor does not have enough pixels to display the image in full at its current size. We say that "the monitor does not have enough pixels" because, again, pixels cover the entire surface area of the screen, and the number of pixels is limited by the size of the pixels.

To clarify, it is equivalent to say that the monitor's pixels are too big to display the image in the fullest possible quality at its current size, because the image's pixel density at that size is greater than the monitor's. The monitor still displays the image in the highest possible resolution, however, and still uses all of its pixels to display the image.


More info

Have a look at this post about image quality and pixel density on Retina displays (2x HD quality of an ordinary HD display). It may help you understand how monitors will "scale" pixel sizes to match the content, while still using all available pixels on the screen.

| improve this answer | |
  • Thanks but I guess I did not wrote the question clear enough at first. Please have a look at the last paragraph which starts with "In short". – Utku Sep 16 '15 at 19:49
  • Yes, I know that monitors will scale the image to fit the screen, thanks for the example. But I wonder how much the power consumption will differ in the case where everything is the same, except PPI. – Utku Sep 16 '15 at 19:53
  • I think you may open a new question: "Will power consumption of two identical screens set to different resolution be different?" and post this answer under that question. This is a good answer and should not be wasted under this question. – Utku Sep 16 '15 at 20:12
  • Thanks, @Utku. Your OP did ask that question, and my answer was addressing that before you clarified by asking about PPI. I agree, that if the original question is asked again this question would do the most good there. – Zachary Kniebel Sep 16 '15 at 20:15
  • You can ask a question and answer your question. Just do it, I think it may benefit future visitors. – Utku Sep 16 '15 at 20:16
1

The power output should be the same since the pixels per inch would be the same assuming the monitors were the same size and aspect ratio.

For instance if you had two monitors that could display 1920x1080 and one was using its full resolution (1920x1080) and the other had its resolution set to 1280x720 the still use the same number of pixels since the 1280x720 would be blown up to fit the screen still using all 1920x1080 pixels.

This is the case assuming both monitors are the exact same size and type (variance in they type of LCD can change it's power consumption.)

| improve this answer | |
  • My question is not this case. It is: 2 monitors, same size, different PPI. – Utku Sep 16 '15 at 19:39
  • If the PPI is different then it is likely the power consumption is different though negligible. They would also have different power consumption if they were operating at the same resolution since the PPI is different. – Automaton Sep 16 '15 at 19:47
  • "If the PPI is different then it is likely the power consumption is different though negligible." If you can back this up with a reference, I can mark this as the accepted answer. – Utku Sep 16 '15 at 19:56
  • "pushing higher pixel densities incurs a cost in the form of greater power consumption for a given luminance value" Pretty simple when you think about it, more pixels = more work = more power consumption. I suppose I should also add that PPI is negligible for a computer monitor not say a cell phone. anandtech.com/show/7743/… – Automaton Sep 16 '15 at 20:06

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.