| quotient of the total radiant flux of all wavelengths emitted by the fluorescent process for an excitation wavelength and the total radiant excitation power irradiating the fluorescent material Note 1 to entry: This quantity is also measured in relative terms by comparison to the radiant flux reflected from the perfect reflecting diffuser identically irradiated and viewed for a given excitation wavelength. Note 2 to entry: Fluorescence is understood to include both fluorescent and phosphorescent phenomena with time constants short enough to be ignored for the application. Note 3 to entry: The spectral external radiant efficiency of the fluorescent specimen has unit one.
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