Eli5: How the finger light thing can tell how much oxygen is in your blood?

Question

As the the title suggests, how is it that a little light they put on our finger when at the doctors/hospital/etc.. is able to tell us our blood oxygen levels?

In: 334

Answer 1

Interesting side note – some SpO2 sensors can’t tell the difference between oxygen bound to hemoglobin and carbon monoxide that’s bound to hemoglobin. So, it’s possible to have CO poisoning, but still have a 90’s-100% SpO2 reading.