Photoelectric plethysmography is a non-invasive technique used to measure changes in blood volume within tissues. It works by shining a light, usually from a LED, onto the skin and detecting the amount of light that is absorbed or reflected. This variation in light absorption corresponds to the pulsatile flow of blood, allowing for the assessment of cardiovascular health. This method is commonly used in medical settings to monitor heart rate and blood oxygen levels. It is particularly useful in devices like pulse oximeters, which provide quick and accurate readings without the need for invasive procedures.