How can I simulate PSF of incoherent light?

Hi There,

Recently, I am working on simulating of Point spread function of high numerical aperture objective lens, according to the Richard and Wolf's mathematics representation, I can do the calculation of PSF, like transverse size or longitudinal size without any difficulty, but this formula is based on diffraction theory, not working with incoherent light. How can I calculate transverse size and longitudinal size of incoherent light PSF ?

Does anyone tell me an appreciate formula or method ?

Thanks
Best regards.

Qinggele