Light sensors in new iPhones confirm their place and importance over fading fingerprint sensors

With Apple’s three latest iPhone*s—the XS, XS Max and XR models—confirming the continued use of 3D facial recognition technology, light sensors and 3D sensing mechanisms are set to become even more prominent.

Apple’s 3D facial recognition will undoubtedly be a boost to the manufacturers of light sensors, as devices whose primary function in detecting differences in the level of light is then harnessed for use in a wide range of consumer, industrial and scientific applications.

Thanks in no small part to the so-called “iPhone Effect”, global revenue for light sensors is projected to reach $1.2 billion next year, up 18% from $1.06 billion this year. As the new applications grow, the market will exceed $1.5 billion by 2022.

Light sensor revenue by application field Light sensor revenue by application field


For fingerprint sensors, Apple’s development spells the beginning of the end. The company’s embrace of light sensors in 3D sensing will send the market for fingerprint sensors into a tailspin.

Ironically, it was Apple that catapulted fingerprint sensors to prominence when the sensors were first used in the iPhone 5S in 2013. But with 3D sensing firmly in place in this year’s iPhone models,  according to IHS Markit forecasts the use of light sensors will effectively kill off the requirement for more than 900 million fingerprint sensors by 2021,. 

Two approaches to facial recognition

Two different and competing approaches are currently used for facial recognition: Structured Light (SL) and Time-of-Flight (ToF) sensing.

The SL mechanism provides greater accuracy in detection, delivers higher resolution, and utilizes less power. However, it requires several components, including a dedicated vertical-cavity surface-emitting laser (VCSEL)—a semiconductor diode—with a dot projector, as well as a near-infrared camera, an accurate component assembly, and high computational resources.

The latest ToF approach makes use of so-called single-photon avalanche diode (SPAD) receivers that can work with any target material and color, although a higher target illumination is required to obtain good accuracy.

For Apple, which has always innovated on its own terms, its idiosyncratic approach sees the iPhone deploy the SL method and combine it with a ToF device. The result is a combination that makes use of the best features of the two, even if the combination is one that is expensive. For Apple, adding a near-infrared (IR) illuminator to its ToF device will enhance the system’s effectiveness under most light conditions while at the same time improving the reliability of FaceID. The result is a more satisfying end-user experience.

Meanwhile, other mobile handset manufacturers such as Samsung, Huawei, Oppo, Vivo, and Xiaomi are rumored to be working on Face-ID-like systems, albeit through a variety of approaches. Some choose to use standard ToF devices, while others adopt a multi-array ToF that is cheaper compared to the full Face-ID set of components and assembly. In many of these Android designs, OEMs are likely including a fingerprint sensor as a fall-back biometric option to their nascent 3D facial recognition system. The fingerprint sensor can either be in stand-alone mode or integrated into the display.

Recently, Huawei announced its first 3D facial sensor in its Mate 20 Pro flagship mobile phone. In addition to providing facial biometrics, the front-facing 3D sensor doubles as a 3D scanner, enabling users to digitize real live objects for manipulation in 3D augmented reality applications. While this is still a novelty application, this highlights the uses of 3D light sensors beyond those of biometrics.

IHS Markit forecasts the ToF market will grow in the coming years, spurred by combo solutions integrated with other light sensors in the same package, leading to a cheaper bill of materials (BOM) compared to an SL BOM.

A further push for ToF solutions could come from technology advancements, such as the one from Swiss-based Senbiosys, a startup tracing its origin to the IMT center for micro- and nano-engineering. Senbiosys claims to offer a new ultra-high-performance chip able to precisely measure ToF. The company’s technology could also mean a higher profile for combo chips, given that the first chip product from Senbiosys was able to simultaneously measure heart rate, oxygen levels, ambient light, and ToF signals. These features are combined with a step improvement in power consumption that leads to longer use of the iPhone between battery charges, or to an improved performance if staying with same power consumption).

Overall, IHS Markit sees a shift in value from an optical assembly-based bill of material being used in 3D sensing applications to a more integrated approach involving multi-array ToF devices. In the new approach, the number of components is reduced, and overall assembly tolerance is relaxed.

Even so, other mobile phone manufacturers are likely to continue using cheap proximity/IR devices for 3D sensing together with a dedicated ToF device for facial recognition. Otherwise, developing specific firmware to use a ToF as a proximity sensor could be more expensive. Another option would be for manufacturers to change display management and adopt a ToF or combo light sensor to perform both basic proximity sensing and 3D sensing.