A new and distinct Gaillardia cultivar named \u2018DGAL906\u2019 is disclosed, characterized by a distinctive crimson red flower, somewhat compact plant habit, good branching and abundant flowering. The first semiconductor regions included in photoelectric conversion elements that are included in each of the photoelectric conversion units and that are arranged adjacent to each other sandwich a second semiconductor region of a second conductivity type. In other arrangements, a track assembly includes two nested tracks, an inner track and outer track.