The characteristics of the Soft X-ray Undulator to be installed on the x-ray ring of the National Synchrotron Light Source are presented. The output of the undulator in the presence of finite electron beam emittance is estimated. The coherence e prop of the radiation are described, leading to an expected partially coherent flux of 102 photons per second. Numerical methods for estimating the irradiance of undulator radiation are presented. The methods use the exact solution for radiation from a single electron and combine the radiation pattern with the electron beam distribution, allowing us to examine cases such as even harmonic radiation on the undulator axis, as well as the red-shift of harmonic peaks due to electron beam emittance. Finally, the effects of electron beam energy spread are briefly considered.