Measurements of the spectral radiant intensity and structure of large turbulent hydrogen diffusion flames, with mass flow rates from 5.4 to 68kg/sec, are presented. These measurements are compared with predictions of the reacting, buoyant flowfield and radiant intensities, utilizing the flowfield and infrared radiation computer codes originally developed to determine rocket and jet aircraft exhaust plume characteristics. The predictions of radiant intensity are shown to be within the data fluctuations (±25%) and the predicted length of the diffusion flame is consistent with the data. However, the predicted flame width is somewhat smaller than that obtained from thermovision measurements of the flame (1.9–3.3 microns). This is attributed to the failure of the turbulence model used in the flowfield code to accurately treat the large density gradients across the flame. It is shown that, for the conditions of these tests, the radiant intensity does not scale linearly with mass flow rate. The ratio of radiant intensity to rate of heat release, F, is demonstrated to vary from 0.153 at very low velocities (small Froude numbers) to 0.086 at the high velocities (large Froude numbers). This trend of decreasing F with increasing velocity is consistent with the experimental observations of Brzustowski et al. 1 The reasonable agreement between the theoretical predictions and data suggests that these codes, and selected laboratory experiments, may be used to develop scaling relations for radiant intensity and flame structure which include effects of optical depth, mass flow rate, velocity, pipe radius, and Froude number.