https://github.com/adafruit/Adafruit_CircuitPython_TSL2591/blob/0fa3c2e585821b8cbeba668e721a8e561ad79b7c/adafruit_tsl2591.py#L252 This should use the ATime reference to determine the resolution for Overflow. If 100 ms, this is >= 36863 counts for an overflow. 37889 observed for saturation in the VIR channel, which exceeds the datasheet value of 36863 (0x8FFF)