We are all trying to save battery here. I don't like to be tethered to my wall outlet or my cars power adapter.
I've found a way to reduce screen brightness (without root) using an app.
I'm used to a pull down notification settings selection, from the ROM on my D1. The best thing I've found that is close without flashing a ROM is "Quick Settings". There are a few options with this app, but I'm only going to touch on one.
The brightness setting in the app has 3 buttons and a slider. The button on the left is minimum, right of the slider is maximum, and far right is auto. The slider adjusts from 0-100%.
Now go to the phones settings screen. Reduce the brightness to minimum there. Now go to a darker area of your house or office and watch what happens when you select minimum in Quick Settings! I'd say you get another 5-7% reduction in brightness!
I hope this gives you a little extra juice for your day!
Sent from my XT862, while on the move.