A spectra generator having an electrically programmable diffraction grating. There may be a broad band light source that emits light which is diffracted by the grating. Diffracting elements in the grating may be individually adjustable so that generation of a specific spectrum or spectra may be achieved. The diffracting elements may be adjusted according to electrical signals of a program from a computer. The generated synthetic spectra may be used for testing and calibration of spectrometers or other devices. Synthetic spectra may also be used for scene generation and other purposes.