The radiant efficiencies of four gas radiant burners were evaluated using total and spectral radiosity measurements as a function of fuel/air mixture and combustion intensity. Ported ceramic tile (C) and steel flame impingement plate (D) burners, with oxidation-resistant downstream steel screens, showed the highest levels of efficiency (53.9% and 52.1%, respectively). A reticulated ceramic burner (B) showed a moderate maximum efficiency (39.4%), and a metal fiber burner 14, without a downstream screen) showed the lowest maximum efficiency (28.4%). At combustion intensities above 250 kW/m(2), burner D exceeded burner C in efficiency, and maintained a close approach to the theoretical maximum efficiency. Design of high-efficiency burners required a combustion product flow pattern around solid surfaces which caused extraction of sensible heat until gas and solid temperatures approached. For burner D, surface temperatures measured by optical means compared sensibly with those from a thermocouple, while graybody emittances were in agreement with literature values. Intense band emissions in spectral measurements of burner A indicated comparatively diminished convection of combustion products to solid surfaces. A mixture preheated to 120 degrees C resulted in a 3.2% increase in the value of efficiency. NOx emissions from Be burners increased with increasing combustion intensity, ranging from 16 to 38 ppm.