A fluorochrome-marked sample is excited with the proper wattage and wavelength
of light using an exciter or bandpass filter and beamsplitting mirror device. This
causes the sample to emit light of a slightly higher wavelength than that of excitation.
A subsequent barrier filter of the proper configuration placed between the sample
and the observer allows this longer wavelength to be observed as fluorescence.
This technique is particularly useful for viewing large biological specimens such
as fish.