The Samsung Galaxy S6 and its curved screen sibling, the Galaxy S6 Edge are two of the hottest smartphones right now. Both combine a solid build quality based on metal and glass and a great performance in nearly every department from the 16-megapixel sensor of the main camera to the display that has more resolution than you'll ever need or even notice. Speaking of which, the Super AMOLED display has been called one of the best displays ever used in a smartphone, not only because of the QHD resolution, the vibrant colors and high contrast that these kind of screens achieve, but because of the high brightness delivered by the ambient light sensor setting, making it readable in most environments including under bright lights. On the other hand, the screen can go as far as 2 nits, making it more comfortable to read in complete darkness and saving battery life (one of the phones weaknesses, by the way) at the same time.
On the software side, the latest version of the TouchWiz UI that's included in these phones was made more simple by trimming down some features that weren't that useful and only slowed down the overall experience. One of the settings that was left out was the one that allowed users to control the behavior of the light behind the two capacitive buttons located under the screen. Since the intensity of those lights is not adjustable, in a situation of almost complete darkness these two buttons can get in the way of reading documents or books because the screen will be very dim and the buttons will light up every time you touch the screen.
Now, here's the solution, there's an app in the Google Play Store called Galaxy Button Lights which will allow you adjust just that. You can choose if you'd like them to stay off completely of if they light up while the screen is on. Also, the app lets you adjust the time the backlight from the buttons stay on. The app is completely free to download and it doesn't require the devices to be rooted, the UI is simple and easy to use with just the necessary controls available. The app is made to work with these two devices, but the developer mentions that it may work with other Samsung devices like the latest Galaxy Note 4.