Spectral data for argon, krypton, xenon, and neon flashlamps are presented for the region of lamp operation in which the line radiation makes up a substantial portion of the total radiant energy. The spectral charateristics are presented in terms of both power flux and emitted quanta per unit area per second, the latter being appropriate for the characterization of illumination and laser pumping efficiencies. The emission spectra show strong line radiation peculiar to each gas superimposed on a low emissivity background continuum. The electrical resistance coefficient is presented for each gas and is shown to increase with increasing gas atomic weight and pressure. An analysis of lamp radiative efficiency indicates that through proper optimization of the gas pressure, the efficiency and overall output of the lighter rare gases will be comparable to those for optimized xenon lamps with optimum pressures increasing with decreasing gas atomic weight. Overall lamp efficiencies are shown to be as high as 40 percent in the region.