| 摘要 |
A two-filament incandescent lamp and operating circuit well suited to lighting applications requiring high service reliability. In the lamp, the rated operating voltage of the second filament is greater that of the first filament. In the operating circuit, there is an inductive reactance in series with the lamp and, in one aspect of the invention, an electrical connection across the lamp terminals for measuring the operating voltage of the lamp. After the power and rated wattage of both lamp filaments have been selected, matched values of inductive reactance and open circuit voltage of the operating circuit can be uniquely determined such that the following advantages are obtained. When the first lamp filament fails, the second filament comes into full brilliance. In a preferred embodiment of the invention, there will be no significant change in the luminous output of the lamp before and after failure of the first filament. A positive indication of the failure of the first filament will be provided via the electrical connection across the lamp terminals. Maintenance personnel, perhaps remotely situated, may replace the lamp prior to failure of the second filament so that service will not be interrupted. In another aspect of the invention, the electrical connection across the lamp terminals is not included in the operating circuit. In yet another aspect of the invention, a method of designing a two-filament lamp and operating system having optimum efficiency is described.
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