(Note; when we talk about “original” screens below, we use “original” to mean those which contain an Apple-manufactured panel rather than a “copy” screen, including unofficially-refurbished ones. This isn’t necessarily the original screen that came with the phone.)
About six months ago, we discussed a problem affected the iPhone 8, 8 Plus and X’s ALS (Ambient Light Sensor) if the screen had been replaced. To cut a long story short, if the replacement screen hadn’t been paired with the phone (i.e. its serial number and calibration data transferred from the original screen), then the screen’s automatic brightness adjustment stopped working under iOS 11, due to the ALS- required to measure how bright the surrounding light is- having been disabled.
