There are many ways and options to adjust Lux - but for me the easiest way to adjust Lux is to simply leave it on "Auto" and then whenever my display is to dim for the "condition" I am in, I simply increase my screen brightness setting to the way I like it - then you simply press a little link button on the display to save those settings.
Once you adjust your brightness level in all the conditions you will be in (it might take a couple of weeks to be in all your different lighting conditions), you will probably never touch Lux again - Lux will simply adjust your screen brightness against all of your background lighting conditions - I thought it would save my battery a little bit and maybe it does?, but it definitely has not hurt my battery efficiency. I always have the perfect screen level and brightness setting for the environment that I am in, and that is a Big Plus! It also switches faster to your preferred setting than the stock auto screen adjustment in any lighting environment you are in.
I hope this wasn't confusing - but it simply works - I bought the paid version to support the developer - the free version works just as well - it doesn't have the auto mode, but that really doesn't matter, because in a technical sense, all the settings are "auto"