OPTICAL MODULE

An optical module (100) for reading a test region of an assay. The optical module comprises: a first light source (101) for illuminating the test region of the assay; an optical detector (103), comprising an optical input for receiving light emitted from the test region and an electrical output; a substrate (104) for mounting the first light source (101) and the optical detector (103); and a housing (105) comprising: a first opening (106) for providing a first optical path from the first light source (101) to the test region (103); wherein the housing (105) and the substrate (104) enclose and positionally align the first source (101) and the optical detector (103) relative to the first opening (106). The housing (105) may comprise one or more legs (108), such as a flexible hook portion which secures the housing (105) to the substrate (104) with a snap-fit engagement, extending from a first and/or second outer surface of the housing (105) in a vertical direction. Beneficially, the snap-fit engagement provided by the flexible hook portion allows the housing to be aligned and secured without the need to use glue or for example a screw and thread that can be difficult to control and/or risks misalignment of the housing.