firefly luciferase catalyzes a reaction that produces visible light in the 550 – 575 nm range. a click-beetle luciferase is also available that produces light at a peak closer to 595 nm. both luciferases require the addition of an exogenous substrate (luciferin) for the light reaction to occur. numerous "luc"-based bioreporters have been constructed for the detection of a wide array of inorganic and organic compounds of environmental concern. the most promising applications, however, probably rely on introducing the genetic code of the firefly luciferase into other eukaryotic cells and tissues.