A light source with a programmable spectral output was designed and constructed following the identification of limitations in current display calibration techniques. Current calibration of a display measurement instrument compares the measured spectral output of a pre-calibrated reference light source with the calibration data traceable to national standards. This allows correction factors to be calculated for each wavelength and entered into the measurement instrument. However, the reference light source used to create these correction factors is very dissimilar in spectral output to test displays such as cathode ray tubes (CRT) or liquid crystal displays (LCDs). The dissimilarity between the reference calibration spectrum and the spectrum of the test display gives errors at some wavelengths, which leads to inaccurate measurement of colour and luminance, and inter-instrument disagreement. The development of a light source with a programmable spectrum, will allow display measurement instruments to be calibrated against a reference source that mimics the spectrum of the device under test, improving the accuracy of measurements and the agreement between display measurement instruments. This paper describes the prototype programmable source and demonstrates the feasibility of mimicking both CRT and LCD spectra. The programmable source could be used as a transfer standard to assess display measurement techniques in international laboratories.