The emissivity values vary greatly with different materials. They are near unity for rough surfaces such as ceramics or oxidized metals and roughly 0.02 for polished metals or silvered reflectors. Emissivity values of commonly used package materials are listed in the table below. Radiation heat transfer is more effective in natural convection environment than in forced convection environments. The effect of radiation can be ignored in forced convection environments. Refer to application note AN-842 for more details on thermal management. For other questions not addressed by the Knowledge Base, plase submit a technical support request.