| 摘要 |
A high intensity discharge lamp (20) includes a pair of electrodes (31, 32) sealed into the same end of the envelope (21), and an arrangement for adjusting the temperature at the wall of the envelope (21) adjacent to the arc supporting electrode rods (33, 34), to minimize the differences in the wall temperature under different orientations of the lamp (20), whereby the luminous efficiency of the lamp (20) is substantially independent of its orientation. As shown in Fig. 2 this may be achieved by providing a groove 81 in the envelope between the electrodes 33,34 such that the ratio L1/L2 of the distances from the arc centreline (i) to the bottom of the groove and (ii) to the envelope adjacent the groove is L1/L2</=1.3. Alternatively, Fig.6, insulating films 24,25 may be provided on the envelope behind the electrodes, the films having a conical angle of 10 DEG -30 DEG . <IMAGE> |
