We describe our application of plasma‐enhanced photoemission as aninsituelectrode diagnostic for operating discharge lamps. The method uses focused low‐power laser beams of various wavelengths to investigate emission properties of cathodes in fluorescent lamps. When a pulsed laser beam is directed onto the cathode, the photoemission effect will cause electrons to be ejected ifh&ngr; is greater than the effective work function of the surface over the area illuminated. This burst of photoelectrons can be monitored, as well as the optogalvanic signal which results as they enter the surrounding discharge and produce additional ionization. The photon energy at which photoemission is observed places an upper limit on the local effective work function, which is influenced by the electric field at the cathode surface.