For those of you who already have Tasker, this can be quite easily done using Tasker as well. For me, I set on auto-brightness but with slider to the max. This suits me for most occasions, except when it's really dark, in which case I find it too bright. So for me I just have 2 simple profiles on screen unlock if the light reading is less than 5, set brightness to 0, otherwise set brightness to 255.
LG G3 32GB LTE
Dopod 838 Pro -> Asus P750 -> HTC Touch Pro -> HTC Touch Pro2 -> Samsung Galaxy S -> Samsung Galaxy SII -> Asus Padfone -> Samsung Galaxy Note II LTE -> Sony Xperia Z2 -> LG G3 32GB LTE -> ??