What are the benefits of using noble gasses (xenon, krypton, argon) for increased life, and how does their use affect cost?

Halogen extends operating life by recycling tungsten, evaporated from the filament and deposited on the inside of the glass lamp, back on to filament coil. It keeps the lamp from turning gray/black and allows brightness to remain at or near initial brightness specs for up to five times that of standard incandescent lamps. Lamps using an inert gas such as argon physically suppress evaporation of tungsten from the filament.

The heavier the atomic weight of the gas used, the greater its effectiveness. This also increases the cost of the lamp, but provides the added benefit of NO reduced life operating on DC voltage, and a whiter, more efficient light that is very desirable where color is a serious consideration. More.

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