The results of fluorescence-labeling experiments may be photographed to produce a permanent record. One of the major hurdles associated with fluorescence photography is that most of the commercially available films have been designed to work at exposure times in the range of 0.0l– 0.1 s. However, the light levels emitted by fluorophores (fluorochromes) are of low intensity, necessitating exposure times one to two magnitudes longer. Low-intensity light over a long period will have less effect on film than high-intensity light over a short period, a phenomenon known as reciprocity failure.