|MadSci Network: Physics|
Since one wants to run an electric current through the filament, it is made out of a good metal. Usually tungsten is used, because of its high melting point. The electromagnetic emission of such a filament in the visible range is dominated by the contribution from the conduction electrons. The vibrational spectrum of the crystalline ions is in the infrared, not in the visible range. The electromagnetic emission in the infrared is usually dominated by these vibrations of the ions. At 300 Kelvin (room temperature) most of the power is emitted in the infrared, so the ionic contribution dominates. But at 3000 Kelvin (which is a reasonable estimate for the operating temperature of a light bulb filament) most of the power is in the visible, so the conduction electrons dominate.
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