The optical sensitivity of SiPM is typically given by the photon detection efficiency (PDE), which is the ratio of detected photo-electrons and the number of incident photons. This value can be used to calculate the responsivity of the sensor by the following equation:
![\[ {\mathrm{R}= \frac{\mathrm{PDE} \cdot \lambda \cdot \mathrm{G} \cdot e \cdot (1+\mathrm{P_{AP}}) \cdot (1+\mathrm{P_{XT}})}{h \cdot c \cdot 100\%}} \]](https://www.ketek.net/wp-content/ql-cache/quicklatex.com-bc5b8bbafbdddeb63829d45fbabe5c01_l3.png "Rendered by QuickLaTeX.com")
= Photon Detection Efficiency
= Wavelength
= Gain
= Electron Charge
= Afterpulsing Probability
= Crosstalk Probability
= Planck Constant
= Speed of light
