History of Incandescent Bulbs
It is fairly well known that Thomas Alvin Edison invented the first
reasonably practical incandescent lamp, using a carbon filament in a bulb
containing a vacuum. Since that time, the incandescent lamp has been
improved by using tantalum and later tungsten filaments, which evaporate
more slowly than carbon.
Nowadays, incandescent lamps are still made with tungsten filaments.
Basic Principles
The filament of an incandescent lamp is simply a resistor. If
electrical power is applied, it is converted to heat in the filament. The
filament's temperature rises until it gets rid of heat at the same rate
that heat is being generated in the filament. Ideally, the filament gets
rid of heat only by radiating it away, although a small amount of heat
energy is also removed from the filament by thermal conduction.
The filament's temperature is very high, generally over 2000 degrees
Celsius, or generally over 3600 degrees Fahrenheit. In a "standard" 75
or 100 watt 120 volt bulb, the filament temperature is roughly 2550 degrees
Celsius, or roughly 4600 degrees
Fahrenheit. At high temperatures like this, the thermal radiation from
the filament includes a significant amount of visible light.
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