Over the last two decades Förster resonance energy transfer (FRET) became a common platform to design protein-based biosensors. The basic idea of FRET-based biosensors is detecting conformational change of "sensing" domains by fusing two fluorescent proteins, FRET donor and acceptor. FRET efficiency has been used commonly to read out the conformational change, which predominantly depends on the proximity between the donor and acceptor. Contrary, although relative orientation of dipole moments is in theory another factor determining the FRET efficiency, detecting the change in angle between donor and acceptor is still challenging. Here I will introduce a new mode of FRET quantification highlighting the angular displacement by monitoring sensitized acceptor anisotropy. Making dim fluorescence donor, Geuda Sapphire, was the key process of developing the new method. We will also discuss efficient FRET from the dim donor.