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We investigated light emission from Au films (2 -90 nm) deposited on highly oriented pyrolytic graphite (HOPG) substrates by excited with a scanning tunneling microscope (STM) in air. STM images indicate that as increasing the deposition, Au films undergo four different configurations, including islands, flat films, film with atop isolated clusters and film with huge surface corrugations. The corresponding intensity in the STM-excited light emission gradually increases with thickness and exhibits sharp peaks, highest one at the thickness of around 40 nm. The monotonic increase in light intensity is attributed to the increase of the electromagnetic field of the local plasmon in the tunneling gap with the film thickness, and the peaks in light emission to enhancement of the local plasmon owing to nanoscale surface configurations.