ABSTRACT
The incandescent lamp represented such a remarkable aggregation of sophisticated technologies–from vacuums to refractory filaments to hermetic sealing–that there was enormous room for improvement. One of the primary problems with obtaining that perfect vacuum was that gases, in particular water vapor, would attach themselves to all the lamp parts. One of the primary problems with obtaining that perfect vacuum was that gases, in particular water vapor, would attach themselves to all the lamp parts. Lamp engineers soon discovered that heat was required to remove the water vapor from the various surface within the bulb. The basic principles of incandescent lamp design predict that the rate of evaporation from the filament determines lifetime. Temperature accelerates the evaporation and thus shortens the life while higher gas pressures slow evaporation and prolong the life. During the mid-1970s, efforts were again renewed to find a simple low cost coating that would provide similar light diffusing as hydrophilic silica but not the inherent moisture problem.
