| 摘要 |
A controller 5 for a high intensity discharge lamp 4 includes a primary ballast for providing a primary current to the lamp 4 , and a current injector which in the case shown comprises a control ballast 8 and a switch 9 (e.g. a triac) controlled by a control unit 12 . The current injector injects a secondary current into the lamp 4 that is less than the primary current and can be varied by the control unit 12 , e.g. by varying the amount of time within an a.c. cycle that the control ballast 8 is switched into the circuit. The controller 5 allows the lamp 4 to be controlled, for example, to operate at a constant power (variable light output) or at a constant light output (variable power).
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