An optical device is provided. The optical device includes a fluorescent wheel, a first light source engine and a second light source engine. The fluorescent wheel includes a fluorescent powder area. The first light source engine provides a first light beam, wherein the first light beam forms a first light spot on the fluorescent powder area of the fluorescent wheel. The second light source engine provides a second light beam, wherein the second light beam forms a second light spot on the fluorescent powder area of the fluorescent wheel, and the first light spot is separated from the second light spot.