Pulse Oximetry is a method that measures how well oxygen is being carried by the haemoglobin in the blood, using two different wavelengths of light.
^^ A Photodetector is just a light sensor which detects the intensity of the light that passes through the finger.
The intensity of the light can depend on the distance it is traveling across and the nature of the medium it is passing through. For pulse oximetry, we are interested in the latter of the two.
In this case, the intensity of the light depends on how much oxygen is being carried by the haemoglobin in the blood. Oxygenated…