A projector arranged to project an image within a display area on a display plane. The image comprises a light feature. A light sensor is spatially separated from the display plane. In an aligned state, light forming the light feature of the image on the display plane is at least partially disposed around the light sensor. In the aligned state, substantially no light forming the light feature impinges on the light sensor. The aligned state defines a selected alignment between the display area and the display plane (i.e. a selected position of the display area on the display plane).