Light-emitting electrochemical cells (LECs) can be fabricated as a single emissive organic/salt layer sandwiched between two electrodes, offering cost-effective next generation signage and lighting applications. Cyanine dyes are especially attractive to exploit the low cost potential of LECs. Cyanines denote a large class of fluorescent organic salts with tuneable emission wavelength, inherent conductivity for ionic and electronic charges, and many cyanines are commercially available at low cost. We systematically tested a set of cyanine dyes for visible emitting LECs. To circumvent non-radiative quenching processes in pure cyanine films (monomer fluorescence quantum yields, PLQE, < 1.5%) we exploited the efficient resonance energy transfer (RET) from cyanine host to cyanine guest molecules (PLQE maximum = 16.2%). The analysis indicated that specific host-guest interactions or a parallel energy transfer channel to host dimers can reduce the guest PLQE, despite a generally high RET efficiency in cyanine host-guest systems. By comparing single component with host-guest LECs, we found that the PLQE enhancement directly translated into the device efficiency increase, and red-emitting host-guest LECs with an external quantum efficiency (EQE) of 0.36% were achieved, close to the theoretical EQE maximum (0.81%). Chemical approaches that provide sterically demanding (to increase the PLQE) and high bandgap (for emission at smaller wavelengths) cyanines at low cost promise further progress in the field.