Anyone remember about 5 years ago when we all learned that using a plain black background would save battery on your smartphone? Pretty funny right? Well it was actually true, but really only for AMOLED displays. Which at the time, Samsung was the only one using them. The reason being, is that lighter colors - specifically whites - would use more power on the display. Which then takes more battery out of your device, obviously. That was on the original Galaxy S which was in 2010. Since then, every Samsung device - except for the Galaxy S4 Active - has had an AMOLED display, and Samsung has been working to make it more efficient while also making the display even more crisp.
It's not quite at the level of LCD displays, but the AMOLED display on the Galaxy S6 is much less power hungry than the Galaxy S4 was. AnandTech did a comprehensive test, showing how Samsung has improved their AMOLED displays in their flagship devices. They tested the Galaxy S4, Galaxy S5, Galaxy S5 LTEA, Galaxy S6 and Galaxy Note 4. The Galaxy S4 which is obviously the oldest, used the most power at 3.41 mW/cd/cm². With the Galaxy S6 using the least at 2.21 mW/cd/cm². Which makes plenty of sense right? Improve the display each and every year. If you look at the Galaxy S4 vs the Galaxy S5, there's actually a pretty large change there.
Samsung's AMOLED panels are still not at the same level as LCD's are just yet. However, the write of the AnandTech report does state that this could be accomplished in the Galaxy Note 5 or even Galaxy S7, late this year or next year respectively. As AMOLED needs to improve by about another 15-20%, to be on par with LCD.
Despite AMOLED using more power than LCD displays, most users still prefer the AMOLED panels, because of the deeper blacks. The AMOLED panel on the Galaxy S6 looks amazing, and is really great for media consumption as well. And if you don't believe us, just ask DisplayMate, who has continuously ranked Samsung has having the best displays out there. Can't be a coincidence can it?