rubin_sim.phot_utils.calc_neff(fwhm_eff, platescale)

Calculate the effective number of pixels in a single gaussian PSF. This equation comes from LSE-40, equation 27.

fwhm_eff: `float`

The width of a single-gaussian that produces correct Neff for typical PSF profile.

platescale: `float`

The platescale in arcseconds per pixel (0.2 for LSST)


The effective number of pixels contained in the PSF

The fwhm_eff is a way to represent the equivalent seeing value, if the
atmosphere could be simply represented as a single gaussian (instead of a more
complicated von Karman profile for the atmosphere, convolved properly with the
telescope hardware additional blurring of 0.4”).
A translation from the geometric FWHM to the fwhm_eff is provided in fwhm_geom2_fwhm_eff.