Light sensors are continuing to evolve from their traditional use in detecting light and distance to include ever-more complex and sophisticated functionality, including 3D sensing and spectroscopy.
3D sensing is one of the strongest emerging new opportunities in semiconductors, while spectroscopy will find increasing use in commercial, military, medical, and industrial applications to determine the chemical composition and molecular structure of materials.
Overall, light sensors help detect different levels of light in appliances, switches, and machines, including light that may not be visible to the human eye, such as X-rays, infrared, and ultraviolet light. Light sensors are also used in scientific, industrial, and consumer applications—as part of a safety or security device, like a garage-door opener; in traffic or outdoor lights; and in everyday consumer electronics such as televisions, remote control units, computers, smartphones, and tablets.
Smartphones are the principal application for light sensors, but wearables and the central display in automotive dashboards will be important sources of revenue as well.
Various types of light sensors
For many years, the principal types of light sensors were ambient light sensors, proximity sensors, color/RGB sensors, and gesture sensors.
Ambient light sensors, which measure the intensity of ambient light in the environment, are deployed to modify the brightness of screens like those in smartphones, with the reduced screen brightness contributing to viewing comfort and less power consumption. Proximity sensors, meanwhile, detect the closeness of an object to the sensor, typically by sensing infrared light; they are mostly used to turn off the touch screen on handsets when the phones are placed close to the head.
For their part, color/RGB sensors measure the color temperature of a given environment and are typically used to correct white balance in displays, while gesture sensors allow proximity sensors to detect hand movements as a means of interacting with devices like phones, PCs, and televisions.
Light sensors can come as a discrete package containing one sensor, even if another sensor component—such as an infrared LED emitter—is integrated; examples would be an ambient light sensor or a color/RGB sensor. Light sensors can also be available as a combo package with two or more sensor functions, such as a 2-in-1 ambient light sensor together with proximity sensor (ALS+PROX), or a 3-in-1 ambient light sensor with proximity sensor and infrared LED emitter (ALS/PROX/IR). The 3-in-1 sensors continue to be the most popular package, especially for the low-end and midrange smartphone market.
Apple and Samsung continue to shape the light sensor market and supplier landscape. In 2016 Apple replaced the infrared proximity sensor with a ToF sensor in the iPhone 7, and in the process virtually reshaped the forecast for light sensors in entirety. Samsung, meanwhile, is the only OEM implementing an optical pulse sensor to monitor heart rate on some of its higher-end smartphones.
The new wave: 3D sensing and spectroscopy
Light sensors are finding their strongest growth potential in 3D sensing and spectroscopy.
In 3D sensing, time-of-flight (ToF) sensors are utilized to detect image patterns, distance, and shape, in the process allowing for a wide range of uses, including facial recognition, augmented reality, and machine vision, for market segments such as home robotics and automotive. The ToF sensor, carefully synchronized with an illuminator, utilizes the light that is reflected by objects in a scene to determine the distance to the objects. The result is a 3D mapping or reconstruction of the object facing the sensor, which can then be used for facial recognition as well as in augmented reality and virtual reality applications.
In spectroscopy, light sensors can measure a range of fluids, gases, and vapors based on the absorption of light by materials at specific wavelengths. Because each material has its own spectral response, the optical signature of a wavelength—or a combination of wavelengths—can be used to identify specific materials and the presence of chemical entities. Spectroscopy can be used in a wide range of applications—in food analysis to measure qualities like water and fat content; in healthcare to detect counterfeit drugs in medication; in industrial and military applications to determine the presence of noxious gases and vapors in the air.