A reference light source (RLS) was designed to allow the measurement and removal of system wavefront errors in wavefront sensing instruments. The wavefront of the RLS is produced by collimating and re-focussing the output of a laser diode onto a 1 micron pinhole aperture. The diverging spherical wavefront is usable over a numerical aperture of .65 for wavelengths greater than 700 nm. To achieve a high quality wavefront, design constraints on the pinhole are quite severe in terms of current technology. Several pinhole fabrication techniques have been explored. Methods for testing pinhole quality include electron microscopy and optical phase conjugation techniques. The wavefront is tested for non-rotationally symmetric wavefront aberrations by rotating the RLS and analyzing the changes in the relevant Zernike terms. Rotationally symmetric aberrations may then be ascertained by comparison of wavefronts measured on several instruments. Methods and results will be discussed in detail.