Coumarins have a wide array of fluorescence emission properties, and are very useful for immunofluorescence. The fluorescence is highly sensitive to the environment of the molecule, more specifically to its microviscosity and polarity. Also, coumarins have a large range of size, hydrophobicity, and shape. These traits make them useful as fluorescence probes of environments such as host cavities, polymers, micelles, and solids. Lastly, the intense blue fluorescence of coumarin makes it easy to distinguish its light from green, red, and yellow light. This is a big advantage during multicolored applications of fluorescence.