It's imposible to measure the relation between oxygenated hemoglobyn and reduced (not oxygenated) hemoglobyn (Hb) without the pair of ir and red lights, is necesary to have this two ligths and receptors for each one light to make a relation between both Hb (oxygenated and reduced) to get a porcentage like 95% of oxygen saturation ( 95% SpO2)

It's imposible to measure the relation between oxygenated hemoglobyn and reduced (not oxygenated) hemoglobyn (Hb) without the pair of ir and red lights, is necesary to have this two ligths and receptors for each one light to make a relation between both Hb (oxygenated and reduced) to get a porcentage like 95% of oxygen saturation ( 95% SpO2)