text: The photophysical properties of the FbFPs are determined by the chromophore itself and its chemical surrounding in the protein. The extinction coefficient (ε) is around 14.200 Mcm at 450 nm for all described FbFPs, which is slightly higher than that of free FMN (ε = 12.200 Mcm ). The Fluorescence-Quantum yield (Φ) varies significantly between different FbFPs and ranges from 0.2 (phiLOV2.1) to 0.44 (EcFbFP and iLOV). This represents an almost twofold increase compared to free FMN (Φ = 0.25).<br />
  The difference to free FMN is even more significant in the case of the photostabaility, the proteins resistance to bleach out during prolonged and intense irradiation with blue light. Based on the bleaching-halftime (the times it takes to reduce the initial fluorescence intensity to 50% upon illumination) the genetically engineered variant phiLOV2.1 is approximately 40x as stable as free FMN. This stabilizing effect can be observed for almost all FbFPs, although it is usually in the range of 5x - 10x.<br />
  The average fluorescence lifetime of FbFPs is in the range of 3.17 (Pp2FbFP) and 5.7 ns (e.g. EcFbFP). They are thereby much longer than the ones of GFP derivatives, which are usually between 1,5 and 3 ns. 
  FbFPs are therefore well suited as donor domains in Förster resonance energy transfer (FRET) systems in conjunction with GFP derivatives like YFP as acceptor domains.