D-Luciferin is used for bioluminescent imaging of living cells, tissues and animal models. The range of applications of the luciferase/D-luciferin system is very similar to that of fluorescent proteins. However, it has the advantage of operating with virtually no background – emitted light is detected in a previously light-free space. In addition, compared to fluorescence-based reporter assays, luciferase-based assays have significantly higher sensitivity and a higher linear range of analysis.