A highly accurate measurement technique has been developed and applied for characterization of the complex transmittance of liquid crystal light valves (LC-LV). The measurement setup is based on a two-beam interference with partially coherent light. An arc lamp light source enables measurements over a large range of wavelengths. We propose a new Fourier transform interference pattern evaluation technique with a high signal-to-noise ratio. Calculations are sped up by FFT algorithms. Measurement results of the complex transmittance are shown for a twisted nematic and a Freederickzs liquid crystal light valve, built in our laboratory.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.