![]() ![]() But he also points to some recent studies that show promising improvements. Although actigraphy can be used to guess sleep duration, it’s not very good at detecting different sleep stages – and it can even think that you've fallen asleep when in reality you're just not moving very much.Įven taking in account modern developments like PPG, Roethslinghoefer estimates that the accuracy of sleep tracking is at about 60%. ![]() Unfortunately, Roethslinghoefer says that sleep tracking isn’t that accurate, especially when it comes to actigraphy. “IR-LEDs are most commonly used for measuring the flow of blood that is more deeply concentrated in certain parts of body such as the muscles, whereas green light is typically used for calculating the absorption of oxygen in oxyhemoglobin – oxygenated blood – and deoxyhemoglobin – blood without oxygen present.” How accurate is sleep tracking with a fitness tracker? “Most common PPG sensors use an infrared light emitting diode (IR-LED) or a green LED as the main light source,” says Roethslinghoefer. How will you know if your tracker uses PPG? Look for a couple of little LEDs on the back of the device. This data can in turn be used to make observations about a person’s sleep, as people's heart rates tend to slow and oxygen levels dip at various stages of sleep. It can use the reflected light to measure things like blood volume and oxygen saturation – but it can also estimate things like heart rate and heart rate variability, by analyzing how much blood is passing through the illuminated spot per second. ![]() Because blood absorbs and reflects different wavelengths of light, the photodetector can take certain measurements from these reflections. ![]()
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