Newer incandescent lighting uses filaments typically made from less fragile tungsten. Materials such as copper or steel aren't practical because the metal has to have sufficient resistance in a short length to dissipate power in the form of light (although incandescent lighting is woefully inefficient: 95% of the power dissipated is heat and only 5% light). Copper or steel could be used, but power dissipated in a resistor is I²R where I is the current and R is the resistance. Since copper and steel have low resistivity, a filament made from these materials would have low resistance and so a much larger current (or longer section of filament) would be needed to create the same amount of power (meaning that supply cables would also have to have to be beefed up).I just checked a table and actually the resistivity of iron doesn't differ hugely from that of tungsten. It's only around half the value. This would mean that a filament of the same length made from iron rather than tungsten would have half the resistance. For the same voltage applied to the filament, current would be double and the power equation would give a value for power consumption of twice that produced for a tungsten filament. Tungsten however has a higher meting point and can become white hot in a lamp, without melting or losing its integrity on supporting wires.
