Eli5: how does the finger clip with the laser at the doctors measure my oxygen level?
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One side of the clip has a light and the other has a sensor. When you clip it on your finger, it shines both red visible light and infrared light through you finger and it hits the detector on the other side after passing through your finger. Hemoglobin is the protein in red blood cells that carries oxygen. Saturated hemoglobin (full of oxygen) and unsaturated hemoglobin (not full of oxygen) absorb different amounts of infrared and visible light, so by comparing the ratio that the sensor detects to the ratio that was emitted, it can tell how much of the hemoglobin in your blood is saturated (carrying oxygen) and how much isn’t.
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