Magnetic fields cause fluorescent proteins in cells to dim. In experiments with human cells, the autofluorescence of flavins decreased by about 3.5% with each passage of the magnetic field every four seconds during 40 seconds of blue light irradiation[1]. For the fluorescent protein mScarlet3 in E. coli, the fluorescence decreased by 21% at a magnetic field of 60 mT[2]. This effect is created by the formation of radical pairs, where the magnetic field affects the spin of electrons, thereby reducing the number of molecules available for light emission[1][2]. At a low magnetic field (around 2.5–3 mT), the fluorescence increases, at higher values it decreases, and at very high values the effect balances out[4]. The researchers confirmed the changes through control measurements to rule out the influence of heat[1]. These findings support a mechanism based on quantum spin interactions with flavin cofactors[2][3].