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Does Apple iPhone X Face ID Have a Sunlight Problem?

October 31, 2017, 3:59 PM UTC

The early reviews on the Apple iPhone X are in. And although many reviewers have been pleased with the device, some have wondered if there’s a quirk with the handset’s Face ID face scanner.

Both Nilay Patel at The Verge and James Martin at CNET reported on Tuesday that when they used the iPhone in “bright sunlight,” the smartphone’s face scanner became “inconsistent.” Patel suggested in his review that he believed the problem had to do with infrared light and the iPhone X not being able to consistently adapt to it.

“I took a walk outside our NYC office in bright sunlight, and Face ID definitely had issues recognizing my face consistently while I was moving until I went into shade or brought the phone much closer to my face than usual,” he said.

Patel’s problem centered mainly on Face ID. Martin, however, noted that the direct sunlight was more of a problem when he was taking selfies with the front-facing camera.

AP technology writer Anick Jesdanun wrote in his own review that “Face ID worked better than expected in bright sunlight,” but added that at times, it wouldn’t work.

Other reviewers, including TIME’s Lisa Eadiccico, didn’t mention the problem.

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Apple’s iPhone X is the first to ship with the Face ID scanner. The technology scans a person’s face to verify his or her identity and provide access to the iPhone’s iOS software. It uses a variety of technologies to achieve that, including sensors and the front-facing camera.

For its part, Apple (AAPL) hasn’t said that direct sunlight would be a problem for its Face ID scanner. In a support page discussing how Face ID works, the company has said only that users should keep the device between 25 and 50cm from, and pointed at, their faces.

An Apple spokesperson pointed Fortune to that support page but didn’t comment directly on the reviews.

So, what might have caused the sunlight problems? Kevin Bowyer, a professor at Notre Dame and expert on biometric technology, thinks that it might be much ado about nothing and something that most users won’t experience.

“I will say that I am skeptical—skeptical that there is any serious performance degradation in any normal ‘direct sunlight,'” Bowyer told Fortune in an interview. “Sure, there is probably something in some extreme conditions—maybe high noon in Death Valley or something. But I will be surprised if anyone had documented any large problem in normal sunny conditions.”

Anil Jain, another expert and professor at Michigan State University, said that “extreme sunlight illumination causes specular reflections on the face that make it difficult for the depth sensor…to accurately estimate the depth.” That, in turn, could technically cause Face ID to break down. But the chances of that happening too often to users appear to be minimal.

Bowyer, for instance, said that if users actually find that direct sunlight is a problem every now and then, all they’d need to do is “have their back to the direct sunlight” and it should work just fine.

So it’s possible that what the reviewers are seeing is purely anecdotal and something that could be easily fixed. It’s similar to Apple’s Touch ID fingerprint sensor, which generally works, but at times, doesn’t register a person’s fingerprint if they mistakenly place their fingers improperly on the sensor.

Apple’s iPhone X, including its Face ID, will be put to the test starting on Friday, when the device makes its ways to customers around the globe. For now, though, there’s no reason to believe the smartphone has a problem in direct sunlight.