This paper presents the results of an experimental and theoretical study of radiation from luminous jet diffusion flames in partial-gravity environments. Tests were conducted for laminar, non-premixed methane flames burning in quiescent air on-board the NASA KC-135 research aircraft for a range of gravity levels. Flame radiation and gravitational acceleration were measured, and flame imaging was performed. The radiation data are compared with those obtained from normal-gravity and microgravity tests, conducted in a drop facility. Effects of g-jitter on radiation measurements are discussed. With the aid of predictions from a numerical model of jet diffusion flames, the influence of gravity on radiation through its effects on the temperature, species, and velocity fields is analyzed. Good agreement between predictions and measurements is obtained.