Color down-converting filters with fluorescent proteins (FPs) embedded in a polymer matrix have led to new bio-hybrid light-emitting diodes (Bio-HLEDs), featuring stabilities of 100 h and <1 min at low and high applied currents, respectively. Herein, the FP deactivation mechanism in Bio-HLEDs at high driving currents is deciphered. Primarily, the nonradiative energy relaxation of FPs upon excitation promotes the release of excess energy to the polymer matrix, reaching 60 °C and, in turn, a significant thermal emission quenching. This is circumvented by changing the device architecture, achieving stabilities of >300 h at high driving currents. Here, the photoinduced deactivation mechanism takes place, consisting of a slow and reversible partial dehydration followed by a quick and irreversible deactivation of the highly emissive ionic form. This is supported by steady-state/time-resolved emission, circular dichroism, and electrochemical impedance spectroscopic techniques. Overall, the limitations of Bio-HLEDs concerning matrix, buffers, device design, and FP stability are highlighted as key aspects to achieve efficient and stable devices.