[en] The hyper-nuclear physics program at JLAB requires an upper limit on the RMS momentum spread of (delta)p/p < 3 x 10^-5. The momentum spread is determined by measuring the beam width at a dispersive location (D ∼ 4m) in the transport line to the experimental halls. Ignoring the epsilon-beta contribution to the intrinsic beam size, this momentum spread corresponds to an upper bound on the beam width of σ_beam < 120 (micro)m. Typical techniques to measure and monitor the beam size are either invasive or do not have the resolution to measure such small beam sizes. Using interferometry of the synchrotron light produced in the dispersive bend, the resolution of the optical system can be made very small. The non-invasive nature of this measurement allows continuous monitoring of the momentum spread. Two synchrotron light interferometers have been built and installed at JLAB, one each in the Hall-A and Hall-C transport lines. The devices operate over a beam current range from 20 (micro)A to 120 (micro)A and have a spatial resolution of 10um. The structure of the interferometers, the experience gained during its installation, beam measurements and momentum spread stability are presented. The dependence of the measured momentum spread on beam current will be presented