Battery life: There’s never enough. Back in the happy days of Nokia feature-phones (“dumb phones”), batteries used to last three, maybe four days between charges. Today, we have fast and powerful smartphones that run out of juice within a day, sometimes less. To fix that, many enthusiasts try reducing their processor’s voltage or clock speed, selectively switching off Wi-Fi, and more – but they’re actually ignoring the single largest battery hog on their device: The screen!

Having your screen set too bright can really drain your battery, and besides, it’s plain uncomfortable. Sure, Android has built-in auto-brightness control, but is there any way to tweak it? Can you change it to be really dim at night or in a dark room? The answer is no, and the answer to that is Lux Auto Brightness.

To Understand Lux, You Have to Understand Auto-Brightness

When you think about it, what’s auto-brightness, really? It’s adjusting the screen’s brightness according to the environment’s light level. For auto-brightness adjustment to happen, your device needs to have a light sensor of some kind (even if it’s the camera pulling double duty), and it needs to poll that sensor for changes and then decide how to tweak the display accordingly. That last part – deciding how to tweak the display – is usually left up to the phone’s programmers, but Lux lets you crack it open and make your own decisions.

When you first launch Lux, you get a nice little introduction. I suggest working through the tour; it’s a few pages of text, but it’s worth the read:

Settings Wizard

Once you’re done with the tour, it’s time to start configuring things; that’s what the Settings Wizard is for.

One problem I had with many ROMs is that auto-brightness just wasn’t responsive enough. I’d pull the phone out from my pocket into bright sunlight, switch on the screen, and would then have to wait for quite a while until the display ramped up. Lux lets you decide how responsive you want it to be, and when it should poll the light sensor. “On wake” (the default) is actually a good choice because it means every time you switch on the screen, the light level would quickly be adjusted. But if you often find yourself going indoors or outdoors while using the phone, you might want to go with Dynamic or Periodic. I went with Periodic for that reason.

The Settings Wizard has a few other steps, including setting Lux’s notification behavior. The default is Disabled, but I recommend toggling that to Enabled so that you always have Lux showing on your system’s notifications menu:

Lux also comes with a widget, and the Settings Wizard lets you pick what tapping it does. Other than that, there’s very little set up to do to get rolling.

The Dashboard

The Lux Dashboard is a slick semi-transparent overlay taking up the middle of the screen. To switch it on, just tap the Lux notification in the notification bar. It shows you the current screen brightness (67% above), and the light level reading associated with it (106 lx). Being able to see the light reading is great for debugging: Sometimes I’m in a bright room and my device reports low light levels for some reason, and Lux lets me see when that’s happening.

You can use the dashboard to teach Lux how you like your brightness:

Slide the brightness bar until the screen is at the level of brightness you like, then hold the Link button until it says “Linked” as above. Lux now knows that in an environment this bright, you like your screen to be that bright. Cooler yet, it can extrapolate: Once you set up a few linked samples like this, Lux tweaks any brightness value accordingly; for example, if it knows you like the screen at 25% when outside brightness is 50 lx and that you like it at 75% when outside brightness is 100 lx, it can figure out what to do when outside brightness is 75 lx (in the middle). So you only need a handful of linked samples for your brightness to act just right.

Sub-Zero Brightness, Night Mode, And Other Paid Features

Lux is free of banners and other annoyances because it has a paid version to support development. That version costs about $2 at present, and it’s well worth each of those dollars. It adds the ability to set your screen brightness extremely low (indispensible at night), and two dedicated screen modes that tint screen colors in a way that’s supposed to protect your night vision (for using your phone in the dark without going night-blind).

All in all, Lux joins Titanium Backup as one of a small handful of Android tools I consider as must-have tools, and gets a spot on our Best Android Apps list, too. Did you try it out? What did you think? Let me know below!