As I found from the datasheet of SDP8371-001 - https://www.icrfq.com/part/3868771-SDP8371_001.html
is a precision Optoschmitt detector molded in a side-looking clear plastic package. The detector is a monolithic IC, consisting of a 0.030 in.(0.762 mm) the square photodiode, amplifier, voltage regulator, Schmitt trigger and an NPN open-collector output transistor. The output is a buffer logic type, switching from low to high when illumination is increased to the threshold irradiance. Detector sensitivity has been internally temperature compensated and laser trimmed for narrow sensitivity range.
Is there any doubt for detector sensitivity? Can anyone help me about photodetector? I'm stuck with it.