A classical laboratory experiment to verify the Stefan-Boltzmann radiation law with the tungsten filaments of commercial incandescent lamps has been fully revisited, collecting a fairly large amount of data with a computer-controlled four-channel power supply. In many cases, the total power dissipated by the lamp is well described by a sum of two power-law terms, with one exponent very close to 4, as predicted by the radiation law, and the other very close to 1, as for simple heat conduction. This result was true even for filament surfaces with a shiny metallic appearance, whose emissivity should vary with temperature.
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