ABSTRACT
Excitation of a sample generates fluorescent light of lower energy and longer wavelength than the impinging radiation. Hence, unless the chemical structure generates a more complex fluorescence, ultraviolet excitation will normally generate a bluish image, whereas blue excitation usually generates a yellowish image. The human eye responds well to bright objects on a black field, so this condition is sought for greatest sensitivity. For fluorescence microscopy, excitation wavelengths are filtered out by a barrier filter for sensitivity and safety reasons. Fluorescence microscope manufacturers usually employ a mercury arc light source that has a wide range of wavelengths for excitation and is equipped with a convenient filter system. The Nikon cube and filter combinations summarized in Table 1 are typical.
