| 摘要 |
<p>An outer prism light guide (48) surrounds a cover (52) which in turn surrounds a light source. Guide (48) is formed of prism light guide wall material having uniform shape in cross sections perpendicular to a first octature symmetry direction (44), with its optical centre line (50) parallel to direction (44). Surfaces of the wall material are substantially in octature relative to direction (44). A surface normal vector (46) at any point on any internal surface of the material is either substantially parallel or substantially perpendicular to a first notional line extending from the point through and perpendicular to optical centre line (50). Cover (52) has cylindrical symmetry about optical centre line (50) to intercept a substantial portion of light emitted by the source. Cover (52) is formed of prism light guide wall material, with surfaces of the cover wall material substantially in octature at any point (54) on cover (52) relative to a second, spatially variable octature symmetry direction (56), which, at point (54), is perpendicular to first octature symmetry direction (44); and, perpendicular to a second notional line (58) extending from point (54) through and perpendicular to optical centre line (50). A surface normal vector at any point on any outer surface of cover (52) is either substantially parallel or substantially perpendicular to first octature symmetry direction (44). Cover (52) is confined to a region sufficiently close to optical centre line (50) to substantially prevent propagation of light rays incident on an inside surface of cover (52) to and through the light guide wall material.</p> |
