The ambient illuminance and light geometry detection system includes a computing process including receiving a hinge angle between two displays of a foldable computing device, illuminance values from illuminance sensors of the displays, and screen activity of each of the displays of the foldable computing device, determining foldable computing device posture information based at least in part on the hinge angle and the screen activity of each of the displays, determining a user facing display of the foldable computing device based at least in part on the device posture information and the screen activity of the displays, assigning differential weights to an illuminance value received from an illuminance sensor of the user facing display compared to an illuminance value received from an illuminance sensor of the non-user facing display and generating an aggregate weighted average illuminance by applying the differential weights to the illuminance values of each of the displays.