Conventional fluorescent lamps are generally constructed fromeither straight or bent glass tubing and have electrodes sealed into each end of the discharge vessel. The electrodes typically comprise a tungsten filament that is provided with a coating of emissive material containign mixed alkaline earth oxides such as calcium, strontium, and barium oxides. While necessary to that type of lamp, the use of electrodes gives rise to significant restrictions inlamp design and performance. Lamp life is limited by the loss rate of the emissive coating, and is greatly influenced both by the type of ballast used and the operatingduty cycle. Typical operating lifetimes of linear fluorescent lamps have a published range of from 6,000 to 20,000 hours when operated on a standard three hour cycle. Cathode life considerations limit the choice of fill gas composition and pressure, as well as discharge current.
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