In this work, we show the results of a control system synthesis of total radiation Radt in an industrial furnace, based on successful nonlinear modeling of this optical combustion diagnostics variable. As a real-life example, we describe the closed-loop solution applied to the case of a ladle furnace preheating process in a steel manufacturing plant. We present total radiation Radt controllers design taking advantage of the nonlinear modeling results, for broad and narrow range controllers respect to the process input of fan speed rate.