https://ieeexplore.ieee.org/abstract/document/8238126/
"""
During measurements, a constant value of 50mA applied to the infrared LED in the sensor while the current value for the red LED was changed between 4,4mA and 20,8mA in discrete time intervals. Reference measurements were taken with a pulse oximeter from the right index finger simultaneously during all measurements. The findings show that the 14.2mA red LED current value provides similar results with the reference device. The measurements taken from the forehead and temporal bones are acceptable when compared to the measurements taken with the reference device.
"""