This PDF is written for low voltage DC halogen lamps:
http://www.walamp.com/lpd/files/applicationnotes/isl297a.pdf It isn't going to apply exactly to ordinary 120V lamps, but the general trends will apply, since the physics is pretty well similar.
The higher the applied voltage, the more current will flow. The greater the current flow, the more heat generated. The more heat generated, the hotter the filament will get. The hotter the filament, the greater the filament resistance. Net result: unlike an idea resistor where current is proportional to resistance, the current in a filament lamp goes up more slowly than the applied voltage.
The higher the temperature of the filament, the greater the light output and the greater fraction of the light output in the human visual range. At higher voltages the lamp will be more efficient.
The higher the temperature of the filament, the faster the evaporation of the tungsten. The lamp will have a much shorter life.
The relations are pretty significant exponentials. If you increase the voltage to a lamp by 10%, expect a decrease in life by something like 25%. The PDF above has approximate equations for the power, light output, and life of lamps.
-Jon
