The present disclosure concerns a drying or heating apparatus that is capable of independently controlling the temperature of the product being heated (e.g., to achieve a desired temperature profile) and the wavelength of the radiation (e.g., to maximize the heat transfer rate). To such ends, a drying apparatus can be provided with one or more heat sources that are movable relative to the product being heated in order to increase or decrease the gap or spacing between the heat source and the product. By adjusting the gap between the product and the heat source, it is possible to control the source temperature in such a manner that produces the desired product temperature and wavelength of radiation.