ˌɛfˈɛm ɪz ðə mˈæksɪməm flʊɹɹˈɛsəns ðæt kæn biː əbtˈeɪnd fɹʌm ɐ sˈæmpəl baɪ mˈɛʒɚɹɪŋ ðə hˈaɪɪst ɪntˈɛnsᵻɾi ʌv flʊɹɹˈɛsəns ˈæftɚɹ ɐ sˈætʃɚɹˌeɪɾɪŋ flˈæʃ.
Fm is the maximum fluorescence that can be obtained from a sample by measuring the highest intensity of fluorescence after a saturating flash.