A lighting device comprises a lamp unit for emitting light, a reflector for reflecting the emitted light, and a housing for accommodating both the lamp unit and the reflector. In one exemplary embodiment, a group monitoring device includes a display configured to display, during an athletic activity, a plurality of individual performance metrics relating to a plurality of individuals engaged in the athletic activity, each individual performance metric relating to one of the plurality of individuals; and an input to manipulate the display. Depending on the affiliation or belonging to a certain cluster, a specific reconstruction algorithm and a specific slab thickness are determined in order to be used for reconstruction of the cluster.