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Can a lamp of the same wattage be used with any ballast rated for that wattage, such as, a 400 W Metal Halide lamp with a 400 W High Pressure Sodium ballast?
No. A lamp will only operate properly when used with the ballast designed for that particular lamp. The lamps to be used with a particular ballast are listed on the ballast label and in the ballast literature. Lamp and ballast compatibility is assured by matching the American National Standards Institute (ANSI) designations for both the lamp and the ballast. Using a lamp that is not specified will affect ballast life, lamp life or both. HID lamps all have specified unique operating characteristics. The ballasts have been designed to operate the lamps within those specified parameters.

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http://www.advancetransformer.com/technical/faqs/faq_high_intensity.asp

Just spotted it.



[This message has been edited by uksparky (edited 07-25-2004).]

If hindsight were foresight, we'd all be millionaires!