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of repetition within the range of seconds for countries which do use "quick lights". This corresponds to frequency of 4 to 24 flashes per minute.
* Have a duration of light less than 2 seconds within each period .
* Have a duration of darkness between two successive flashes being three times or more the duration of a flash . For example, if the frequency is 20 flashes per minute (period of 3 seconds), the duration of a flash may be 0.75 seconds and duration of darkness following may be 2.25 seconds to satisfy constraint .

If

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