The carbon filament will incandesce more. The reason for this is that the resistances in carbon and metal filaments depend on temperature in different ways: the resistance of a carbon filament decreases with an increase in temperature, while that of a metal filament increases. At normal incandescence both
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bulbs have identical resistances (since their power is the same). Therefore when they are connected in series—when incandescence, and consequently the temperature, of both filaments will be lower than normal—the resistance of the carbon filament will be greater than that of the metal filament; therefore the former will incandesce more (its fall of potential will be greater).