Reflection versus fluorescence: a note on the physical backgrounds of two types of light microscopy.

Bright microscopic images against a dark background can be originating not only from fluorescence, but also from selective reflection. Selective reflection or scattering of visible light in microscopic preparations can be used for the visualization of sometimes otherwise barely distinguishable material. The images obtained superficially resemble those from fluorescence microscopy. They do not, however, result from huminescence but from selectively reflected light with wavelengths in the region of the absorbance peak of the chromophore present in the stained biological material. The respective backgrounds of the underlying physical phenomena and the conditions under which selective reflection can occur are discussed.