This paper gives a detailed analysis of the radiation terms in the heating balance for overhead conductors. The terms in the radiation balance determine the rating of an overhead line for use in dynamic line rating schemes. These radiation terms are often not considered and in which there is a relatively big uncertainty. The available knowledge and the different uncertainties are summarized, for radiation from the environment reaching the conductor, for thermal emission from the conductor and for heating of the conductor due to direct and indicated solar irradiation. The impact of the uncertainties on the uncertainty in line rating is quantified and it is concluded that the error made is around 10 % for low wind speed.