[Samsung Galaxy Nexus] Davidsmonkeyroost:
Hello all,

I've been suspicious of the power draw of the screen on the GNex, and so decided to figure out how much a difference brightness made.

This is to test the difference extreme brightness settings make to battery run times. Including text, browsing or having radios on will dilute the results. I'm only interested in the efficiency of the screen and its supporting infrastructure people! :-)

Here's my testing method.

1. Charge phone to 100% using a PCs USB charging (should give a more full charge than the wall adapters quick charge, I think, otherwise no harm done). Leave attached to USB cable

2. Switch the phone into Airplane mode.

3. Switch off Auto Brightness and turn brightness to Max

4. Restart Phone. Leave it to settle for a few mins

5. Fire up "Just Pictures" and the image "TotalWhite.jpg" (attached). No other photos in the folder where it sits.

6. Disconnect USB charging

7. Start Slide show. Record the start time.

8. Every now and then (about 45 mins to an hour and bit) I quickly pop into settings and take a sneak look at charge level - don't want to get caught out!

9. Resume Slide Show.

10. Wait until the phone switches off, which is less than 2% charge
​

Now, it's not a quick process as I'm going from 100% Batt until auto shut off. So I'll be updating this post in installments. Today is the Max Daddy Full Brightness White image!

Full Brightness, White Image:

100% 00h00m

85% 00h39m

60% 01h53m

35% 03h08m

0% 05h00m​

Pretty good I think!

Battery status stated that Screen was 91% and Android System was 9%. Screen on time was the same as the run time. It never went off.

There's a heavy set of disclaimers to go with this though:

The White Image isn't quite the right aspect for it to display across the full amount. Check out the image "White Full The Phone.jpg" - it's pretty close though. Just Pictures isn't so full screen that it takes over the Android buttons - Anyone know a 100% full screen picture view BTW? Between the point where it comes up with "Please connect your charger" (15%) and 6% it said that message over the White image and partly dimmed the screen - I'm at work and was in the middle of something when it happened.

Minimum Brightness, Black Image:

100% 00h00m

85% 01h26m

82% 02h05m

18% 08h54m

0% 10h47m​

Battery status stated that Screen was 85% and Android System was 16%. Yes, that's 101%, but there you go... Screen on time was within a minute of the run time.

Again, some notes on the testing:

From the "connect your charger" point (i think 15%) to 8 % it had the message on the screen. Just before the end I accidently touched the screen and ended the slide show for up to 15 minutes and the screen went off. Switched it back on and it was at 2%. It then lasted something like 30 mins before auto shutdown. Black isn't Black! check out my the photo "Black Dim The Phone.jpg" - ignore the strange black specs, it was 1 seconds exposure at F1.4, with the camera facing down - think there's some crap in my camera body/lens.

Minimum Brightness, White Image:

100% 00h00m

0% 10h20m​

Again, Battery status stated that Screen was 85% and Android System was 16%. That's the same as when I ran it on Min Brightness, Black Image...

Maximum Brightness, Black Image:

100% 00h00m

0% 10h52m​

Battery status stated that Screen was 90% and Android System was 11% (again 101% also probably due to some rounding going on). Screen was on 100% of the time, Android OS was awake for 100% of the time, CPU time 23 Seconds

Overview:

Maximum Brightness White Image: 5h00m

Maximum Brightness Black Image: 10h52m

Minimum Brightness White Image: 10h20m

Minimum Brightness Black Image: 10h47m

Well, well, what's happened here? Maximum brightness with a black image scored the longest run time - unbelievable, right? Yeah pretty much: On the minimum brightness black run I did check the battery stats a few times. The black image run had a greater Android OS drain (11% vs 9%) compared to the white image. As I switch the phone off in preparation for the test it's possible I inadvertantly bump charged the phone. In addition to this, I was trusting the phone a lot more in this, the final test and didn't check the battery status near the end, so perhaps drawing a lower current happily sitting there doing nothing other than displaying a blank image the phone managed to syphon off the last dregs of power, as opposed to spending CPU time with me rummaging through the settings screens for battery stats. Let's put it all down to being in the margin of error and consider the Black images to have the same run times, despite the Android buttons blazing away on Bright (but they aren't many pixels).

Conclusion:

Back to my original concern, that the screen was abusing the battery more than necessary. I'm mostly happy with the outcome - Black bright and dim screens draw substantially less than a very bright white screen on this phone, as it should. It's surprising to see that on dimmest setting the white screen got so close to the run time of the black screens. It's producing a lot more light than either black screen. It's drawing c5% more power than the black screens, but I would expect a lot more. I'm guessing that the circuitry to run the Screen and the small amount of power used to make the "Black" OLEDs glow dark dark grey draws only a little less than the white screen.

And that's a shame. I wanted to run an app such as "Off-Clock" to have a clock on the screen like the Nokia N8 used to do, but i'm thinking this will eat the battery in 10 hours 20 minutes. Only one way to know for sure....

My initial annoyance that Black never is actually Black whilst the screen has faded. Many of you good folks have pointed out (and after more Googling) that all OLED screens have this, although the reason for it isn't clear. It's either to ease the transition from black to lit by having the LED at the threshold already, power seeping into the circuit somewhere or something else. Who knows, maybe we'd get better run times if the screen was on full brightness but used PWM or a fast strobe to show a dimmer image!

That's all folks, discuss, and remember - continue testing...