The microwave oven was invented in 1945 by American engineer Percy Spencer. He discovered the heating effect of microwave energy accidentally when a candy bar in his pocket melted while he was working with a radar set emitting microwaves. Spencer then experimented with this effect, leading him to file the first patent for the microwave oven in 1945. The first commercial microwave oven was sold in 1946, but residential microwaves only became popular and widely available starting in the 1960s and 1970s.