Apple is using a secret facility in California to develop MicroLED screens for the Apple Watch and iPhone, Bloomberg reports, with plans to replace third-party OLED screens in several years. Developed under the code name T159, the MicroLED screens are said to be notably brighter and superior in color accuracy to OLEDs, and should enable Apple to build thinner, lower-powered devices. They are also expected to offer superior contrast and response times, which could enable deep blacks, bright whites, and smoother animations in Apple’s smallest devices.

According to the report, Apple’s Santa Clara facility is currently capable of manufacturing a handful of Apple Watch-sized screens at a time and will scale up the process over the next two years so that either contract manufacturers or Apple itself can produce the screens in mass quantities. Three hundred engineers are currently working on the project in a 62,000-square-foot space. Based on the factory’s current progress, “consumers will probably have to wait a few years” for the screens to appear in Apple Watches, and it’s “unlikely that the technology will reach an iPhone for at least three to five years.”

The MicroLED manufacturing process is said to be “extraordinarily complex,” as millions of individual pixels each have red, green, and blue sub-pixels that must be individually created and calibrated. LEDs are “grown” in a lab and individually placed inside each screen from “donor wafers,” a process Apple was initially unsure it could scale to the demands of its devices.

The company acquired some of the intellectual property related to the process in 2014 from a startup called LuxVue and subsequently set up facilities in both Taiwan and Santa Clara to determine whether it could manufacture screens on its own — engineers and executives only recently concluded that it could. The company subsequently allowed its engineers to publicly participate in a large number of sessions at Display Week, a Los Angeles event devoted to screen technologies, and it will likely be recruiting new talent there.

Apple plans to expand its use of OLED screens until MicroLED is ready for market, going from one iPhone model to two and adding LG as a second supplier alongside Samsung. The Apple Watch will continue to use OLED until that time, as well. However, news of the shift from OLED to in-house displays has roiled stocks of Apple’s existing screen suppliers across Asia.