Light sensors on wearables struggle with dark skin and obesity

Light sensors used to track heart rate in wearable devices like the Apple Watch Series 5 and the Fitbit Versa 2 don’t work as well on darker skin or people with obesity, according to modeling done in a new study.

That’s a problem for features currently built into devices — but it’s also a bad sign for efforts to use light sensors for new applications in wearables, like monitoring blood pressure, says study author Jessica Ramella-Roman, an associate professor studying bioimaging sensors at Florida International University.

“The architecture of the device has to change,” she says.

The study looked at the photoplethysmography (PPG) signal, a technique that uses changes in how light is reflected to measure blood flow, on three wearable...

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