I believe the problem lies in the terrible light sensor that we have in the S4.
Download
Phone Tester from the play store and select Sensors Status.
Then scroll down to see the value of the light sensor.
It's daylight outside (7:30am), and have have daylight coming into an unlit room (too tight to pay for electric) However, the sensor still reports 0. I wouldn't even describe my current lighting conditions as dark.
0 should be the value it returns in pitch black.
The sensor needs quite a bit of light to even start registering in the first place.
Its the brightness setting in this large grey area that causes all our problems.
In light-ish conditions (when this is still reporting 0) then a dim setting can look exactly that.
So if this is upped, then it looks much better under these conditions.
However, in extremely dark conditions this setting looks much too bright and can cause eye-strain, so the dimmest setting for the screen is then much better.
I think this is why there has been so much discrepancy in the brightness settings. Some say the original updated CM values are great (myself included) others say its too dim. This is probably because the ones who prefer it usually operate in darker lighting than the ones who didn't like it.
