| 摘要 |
PURPOSE:To improve quality and reliability by reducing the functional deterioration of a light transmission plate and the shape deformation of the plate. CONSTITUTION:The light transmission plate 11A is constituted so that notched parts 11a, 11b, 11c and 11d formed by removing four corners of the plate 11A in the shape of a nearly triangle may be separately arranged. That is, the corner parts corresponding to electrode device parts 4 of discharge tubes 121 and 122 which are arranged in tight contact with the plate 11A are not formed on the plate 11A, so that gap parts are formed between the end parts of the notched parts 11a, 11b, 11c and 11d and the electrode device parts 4 of the discharge tubes 121 and 122, then, the plate 11A is thermally separated. |
