Intensity and duration of iPhone 6 and 6s camera flash LEDs

W'ere trying to set policy on allowing or not, digital camera flash photography on art museum paintings displayed at low illuminance, (a major West Coast art museum). But to have a clearer idea of the calculated risk one has to know the default duration and luminous flux (lm) of the flash for either one or both of the backward facing camera LEDs at a standard 1 meter distance. Does anyone have this specific data?