Abstract: Various embodiments include methods and systems to calibrate a gain of a photodetector. A method can include providing, by a reference light source, first light to a reference photodetector, determining, by controller circuitry, whether a first value from the reference photodetector produced in response to the first light is within a range of acceptable reference photodetector values, in response to determining the first value is within the range of acceptable reference photodetector values, providing, by the reference light source, second light to a measurement photodetector, determining, by the controller circuitry, whether a second value from the measurement photodetector produced in response to the second light is within a range of acceptable measurement photodetector values, and in response to determining the second value is not within the range of acceptable measurement photodetector values, adjusting a gain of the measurement photodetector.