My new iPhone 5 screen dims badly and has difficulty waking up

First of all, my auto brightness is off.

I took my phone out of my pocket, went to unlock it and only the backlighting was on, so it was only lot up 20% of my settings. I unlocked the phone and was able to flip through my app screens, yet the actual screen never "woke up".

I went to the brightness screen in the settings and moved the setting slider just 1mm and the thing woke up fully. So strange. What could have caused this?