Calculate the fluorescence index (FI)
Interpolation
Different excitation and emission wavelengths are often used to measure
  EEMs. Hence, it is possible to have mismatchs between measured wavelengths
  and wavelengths used to calculate specific metrics. In these
  circumstances, EEMs are interpolated using the
  interp2 function from the parcma library. A
  message warning the user will be prompted if data interpolation is
  performed.
Examples
file <- system.file("extdata/cary/scans_day_1/", "sample1.csv", package = "eemR")
eem <- eem_read(file, import_function = "cary")
eem_fluorescence_index(eem)
#>    sample       fi
#> 1 sample1 1.264782