An experimental investigation of interaction of free convection and radiation in a horizontal fin array is carried out. A differential interferometer is used to obtain free convection heat transfer and radiation is calculated by solving the integro-differential equations numerically. Results are presented to show the effects of various parameters such as emissivity of the fin surfaces, fin spacing, fin height and base temperature. Correlations are suggested in terms of non-dimensional parameters, based on a large number of experiments. The main conclusion to be drawn from the present study is that radiation-convection interaction invalidates additive approaches in which convection and radiation contributions are independently calculated assuming all surfaces to be isothermal and then adding these to obtain the total heat loss from the fin array.