In order to obtain the influence of the luminance at photopic level on the neural mechanism,a neural contrast sensitivity function(NCSF) measurement system is established.The contrast sensitivity function(CSF) of the visual system and the modulation transfer function(MTF) of the eyes optical system are first measured with correspondent instruments respectively.Then the NCSF is caculated as the ratio of CSF to MTF.Four individual eyes are involved in the cases of green light and white light.With increasing luminance,the tendency of the variation of the CSFs is similar to that of the NCSFs,while the gain is larger than that of the NCSFs,especially in the region of higher spatial frequency.It is the NCSF,rather than CSF,that reflects the luminance sensitivity in the retina-brain neural system,because the influence of the eyes optical system is excluded.