The assumption has often been made that the ratio of the emergent nadir 1304-¿ intensity to its column production rate is equal to 2. Based upon the arguments used, the value should have been closer to 4. The actual value, however, depends strongly on the photon source distribution in the medium. This has been demonstrated by solving the radiative transfer equation for a variety of photon source distributions. In the presence of pure absorption by molecular oxygen the ratio was found to vary from less than 2 for deeply embedded sources to 3.6 for sources peaking near 450 km. For the UV tropical airglow the ratio lies between 3 and 4, and this resolves the long-standing problem of why the tropical 1304-¿ nadir intensity is about twice the corresponding 1356-¿ intensity.