The sensor, the TCS3701, can pick up both visible and infrared light, AMS said. The key development is the ability to ignore light produced by the OLED panel, registering only outside sources.
Ambient light sensing is one of the reasons for the "notch" on the iPhone X, XS, and XR. Without an ambient sensor the phones would be unable to automatically adjust brightness or white balance, or shut off the display when it's held to a person's ear.
When the iPhone X launched in 2017 the notch was one of its biggest criticisms, given that it interrupts what is otherwise an edge-to-edge OLED panel. The core reason for the design choice was the TrueDepth camera used for Face ID and animoji, which has carried over to the iPhone XS and XR.
Some companies, like Samsung, have actively striven against incorporating notches, while others have embraced or even deliberately imitated Apple's concept. The possibility opened up with improvements in OLED manufacturing.
Many iPhone owners have got used to the notch, but it's speculated that Apple's 2019 iPhones could adopt a "hole punch" for their front-facing cameras, maximizing usable screen area. A hidden ambient sensor could make that idea more practical.