Many of the top flagship phones use AMOLED display technology, and the popular wisdom has always been that you can save substantial power on these devices by using apps with a black interface. Is that actually true with a real device, though? With Samsung's Galaxy S5, Galaxy Note 4, the new Moto X, and even the upcoming Nexus 6 all using AMOLED panels, it's worth knowing if you can stretch the battery a little longer by losing the colors.
Where AMOLEDs Shine
The theory of why AMOLEDs use less power when displaying black makes sense when you understand how the technology differs from and LCD display. LCDs like the ones you find on the LG G3 or HTC One (M8) produces light with an LED backlight. The light shines through the pixels and into your eyeballs. In this case, a black pixel is simply one in which the pixel has turned opaque—it blocks all the light streaming in from the backlight. The backlight is still on just the same.
An AMOLED doesn't have a backlight at all. Instead, each little sub-pixel is like a tiny red, blue, or green colored light. If the screen is instructed to display black, it doesn't need to block any light, it simply doesn't light up any of the little colored sub-pixels.
So theoretically, black pixels save you a lot of power because those pixels can be turned completely off. However, people sometimes make the mistake of thinking this is a function of brightness—that dark colors like gray are similarly efficient. There is a relationship between brightness and power, but to really save juice you need a true black (as defined by the #000000 hex value). Anything else, and the pixel is on.
As an added bonus, AMOLEDs have fantastic contrast thanks to the way they produce light, so text is very crisp when using a black background. The catch is that AMOLED screens typically use a bit more power than modern LCDs when displaying bright colors, especially white (where all the sub-pixels are fully lit up).
The question is, does a modern AMOLED still offer noticeable battery savings when using apps made with AMOLED-friendly black background options?
To make any conclusions about AMOLED power consumption, we need data. I used a 2014 Moto X and acquired data with app that simply logs the total current drawn from the battery (in mAh) as reported by the Android OS. There is no reliable way to isolate only the power consumed by the screen, but we don't need exact values to know if there's a big difference in real-world power draw. All that's required to reach a conclusion is the difference between total power consumption with black and non-black apps (if there is one).
To get anything valid data for this test, I tried to reduce the variables as much as possible. Using the Android developer tools, I disabled all background processes, turned off syncing, and placed the device into airplane mode just to be safe. The screen was locked to 50% brightness and timeout was also set to 30 minutes—the duration of each test.
I used Reddit Sync for the test as it has an easily accessible AMOLED mode. The system monitoring app was set to log the power draw once every 60 seconds and was allowed to run for 30 minutes until the screen shut off. I ran this with Reddit Sync in AMOLED mode and again in regular mode. The screen isn’t all black in AMOLED mode; there’s still content on it, but this is a more realistic scenario.
The chart above has a sample of the first 10 data points from each run, as well as the overall average power consumption of all 30 measurements. You can see pretty clearly that in this case, a black screen does indeed reduce how much juice the phone is using. Power consumption was 41% lower overall when using the predominantly black interface in Reddit Sync.
So what does this mean for your phone's battery life? You can definitely make a dent in battery drain with predominantly black apps. If you use a device heavily, the display will be at the top of the battery usage list, so the impact can be noticeable if you keep to AMOLED-friendly apps most of the time. Your actual savings will depend greatly on how much screen time you have and which apps you use, but eking out an extra 15 or 20% screen time seems quite plausible.
On today's modern high-end phones, using predominantly black AMOLED-friendly apps might could easily give you an extra hour of screen-on time, which is nothing to sneeze at.