That's one helluva gamble.
Assuming that light from another world reaches us - having completely avoided dust, comets, meteorites, rings of rocks which surround star systems, the stars themselves - there's still no way to tell how old the light would be and therefore impossible to determine it's origin. Afterall the universe is still expanding. It would be like NASA holding a big conference saying how they're something like 25% sure that someone just pointed a torch at us but can't be sure of where it came from...
Besides, who's to say that an alien civilization uses light bulbs? Glowing green rocks never go out of fashion on alien homeworlds! /ttiforum/images/graemlins/smile.gif
James