An apparatus for electrostatic spray coating of the insides of light transmissive lamp envelopes, comprising a stand, a turntable mounted on the stand for receiving pairs of the envelopes, gas burners for preheating the envelopes and burning in the sprayed coating layer and serving as an electrode to ground the envelopes, a dust generator for preparing and homogenizing, with a rotary chopper, the particles of the dust to be sprayed on the envelopes as the coating layer, spray guns with dust conduits connected to an exhaust system for collecting the particles of dust not bound in the layer and made free during spraying. The apparatus further comprises an electrostatic voltage source connected to the nozzles of the spray guns for negatively charging the dust particles so that the particles are electrostatically attracted to the envelopes, and elements to allow cleaning of the apparatus.