An electronic device may be provided a plasmonic light sensor. Plasmonic light sensors may include arrays of plasmonic image pixels that detect evanescent electron density waves, or plasmons, generated in the plasmonic image pixel through an interaction with incoming light. Plasmonic image pixels may include microlenses that focus the light onto conducting wires in the plasmonic image pixel. Plasmons generated on the surface of the conducting wire may propagate along the conducting wire. Detector circuitry may be coupled to the wire on which the plasmons propagate to detect the light through detection of the evanescent electron density wave. Detector circuitry may include a biasing component for biasing a photodiode such that a small amount of light results in an avalanche of charge, or a sudden increase in current, produced in the detector circuitry in response to the evanescent wave.