What Exactly is the ALS Sensor?
ALS stands for “ambient light sensor”. Basically, this is what the iPhone uses to detect the levels of ambient light, then in turn adjust the brightness of the screen to match those conditions.
What Does This Have to Do With Replacement Screens?
Most people don’t even notice the automatic adjustment of the screen brightness in everyday use. This, after all, is pretty much the point. There’s a good chance they won’t immediately notice when it stops working either, though they might eventually twig when they realise the screen appears uncomfortably dim in daylight or unpleasantly bright at night.
The problem is this- if you change the screen on an iPhone X, 8 or 8 Plus that’s still running iOS 11, then the ALS sensor- and automatic brightness adjustemnt- will stop working. Makes no difference whether the replacement is also an original or if it’s a copy. In fact, even if you swap out the entire assembly from another iPhone (including its ALS sensor)… still won’t work.
This is because, while it’s booting, iOS looks up the serial number on the installed screen and checks it against the number of the one that was calibrated to the phone at the factory. If they don’t match, the ALS sensor gets disabled.
It’s known that the check only happens during the boot process because, if one hot-swaps the original screen after the phone’s finished booting- and while it’s still powered up and running normally- the sensor will continue to work until the phone is rebooted. (Not that we actually recommend this- as you probably know, changing the screen or doing anything similar while the battery is connected stands a good chance of damaging the phone).
Getting Around the Problem
Originally, no-one but Apple could do anything about this, but specialised devices that could transfer the serial and calibration data from one screen to another quickly appeared on the market. (You can see the one that we own in the images).
This device reads the data from the old LCD/OLED screen and writes it to the new one. (It only works with originals, as copies don’t contain the original IC in the first place).
A possibly annoying “gotcha” is the fact that if the screen has already been replaced previously, but whoever did it didn’t transfer the serial/calibration data, then transferring the data from that to your new screen won’t help much.
Here Comes iOS 12 To The Rescue!… Or Maybe Not.
When the beta of iOS 12 came out in June of this year, it seemed that the issue had been fixed- ALS and auto-brightness adjustment worked even if the serial hadn’t been matched using the programmer device. There was some concern that this fix wouldn’t make it into the final release, but the good news is that it was retained with iOS 12.0, officially released last month.
We say “good news”, well… not quite. It turns out that the True Tone feature which automatically adjusts the colour balance– as opposed to brightness (and which wasn’t affected by the ALS issue under iOS 11) now doesn’t work under iOS 12 unless the serial/calibration data has been transferred.
On top of this, the possibility exists that Apple could withdraw the aforementioned fix in a future update- which would cause ALS on any iPhone 8, iPhone 8 Plus or iPhone X with a non-serial-matched replacement screen to stop working again! If you’re in the repair industry, there’s a good chance you’ve already realised how big a problem this could be for you- customers bringing back phones that you’d already repaired and assumed were okay, because the ALS stopped working after an update.
(Since we own a reprogrammer, this means that any such original screen replacements we carry out on your behalf don’t carry the same risk of that happening! Please contact us if you’d like to find out more about this and other services we offer.)
It also draws attention to the fact that Apple can tell- without having opened the phone- whether or not the screen installed is a replacement… just by reading that data. It’s possible they could deny service on this basis- who knows?
Both are possible concerns for both end users and for those working in phone repairs.
Transferring the calibration and serial data from the original screen into the programmer.
Moving the data over to the new screen.
