Systems and methods for generating, projecting or correlating thermal spectra use digital micro-mirror devices (DMDs) to controllably modulate input radiation such as long wave infrared light. An optical system for creating an output spectrum based upon an input light suitably includes a grating configured receive the input light and to spread the input light by wavelength into an input spectrum. A digital micro-mirror device (DMD) is configured to receive the input spectrum and to controllably activate mirrors in the DMD corresponding to selected wavelengths of the input light. Portions of the input light having selected wavelengths can be extracted from remaining portions of the input light for the output spectrum. By selecting and activating only certain mirrors on the DMD, particular wavelengths of light in infrared or other spectra can be optically switched for any number of subsequent applications, including spectral projection, simulation of solar or other spectra, detection of chemical substances, or the like.