2 AMOLED devices have very different screens, faulty device or faulty information?

[347dev]

i'll preface this question with an informative nomer, i am in the market for new displays, not only phone but monitors, laptops and televisions as well but i have hit what appears to be a wall about understanding display capabilities, my example for you is as follows;

i have 2 devices that claim to be using the same technology in their screens, the samsung galaxy s3 and the samsung galaxy s5. they are both AMOLED (well the s5 is super AMOLED but to my understanding that just means the digitizer is not a seperate component, something that does NOT effect the issue i am faced with) long story short if you were to put a black image on both devices the s3 remains bright and the s5 appears off... the screen isnt actually off on the s5, lets imagine a color image centered on its screen black surroundings, the surrounds have no detectable light , the same image on the s3 would have an illuminated background.

hearin lies the problem, how do i know (sight unseen) if a device will have perfect blacks if i am getting a new phone, laptop, monitor, television, ect? especially when the only information availible to me on devices i know are different are described as the same?

PS-please excuse my disregard for capitalization and punctuation, grammar in general

 

[347dev]

i guess this isnt the right place to ask, if anyone would point me to the correct corner of the internet; consider my appreciation forwarded