An optical assembly includes a light-emitting device, a partition structure and a cover. The partition structure defines a first space for accommodating the light-emitting device. The cover is disposed over the partition structure. The cover has a first surface facing the partition structure and a second surface opposite to the first surface. A light emitted by the light-emitting device forms a first irradiance pattern projected on the second surface of the cover, and the first irradiance pattern includes a first dark zone traversing the first irradiance pattern.