A housing includes a first tubular portion being tubular, arranged to extend along a central axis extending in a vertical direction, and having a first cavity defined radially inside of the first tubular portion; and a second tubular portion being tubular, connected to a lower portion of the first tubular portion directly or indirectly, and having a second cavity defined radially inside of the second tubular portion. The first cavity is arranged to define a light path along which the incoming light travels, and is connected to the second cavity. The second tubular portion is arranged to house at least a portion of the optical component therein. The first and second tubular portions are defined by a single monolithic member.