I've had my Xperia U for about 5 months now. It's an interesting phone, it's a nice shape but Sony have done bad things to Android and it frequently plays a fun game where it goes so slow that it doesn't wake up in time for me to answer a phone call before it goes to voicemail... Anyway, one of its less desirable features is the silly light bar gimmick across the bottom of the device, all it does it use up battery and make the phone painful to use in the dark.
But! Today, I stumbled upon a way to (mostly) disable it (apart from in the gallery/album app). Install the following app from the Google Play Store:
Google Play Store: Illumination Control
And then in the app's settings, go to "Set Theme Color" and then slide all the sliders all the way to the left, you might have to wiggle them a bit first if they are already in that position.
It's that easy! Now you can use your phone in the dark without being blinded!