| 摘要 |
PURPOSE:To improve the light emission efficiency and to maintain the film strength of a fluorescent material layer by reducing the grain size of an ultraviolet ray reflective material gradually from an ultraviolet rays source toward the remote fluorescent material layer. CONSTITUTION:A fluorescent layer 7 of the first layer applied onto the inner face of a housing 5 is formed by mixing an ultraviolet ray reflective material 2 having smaller grain size then conventional one into normal expensive fluorescent material 1. While a fluorescent layer 8 of the second layer to be applied onto the first fluorescent material layer 7 is formed by mixing an ultraviolet ray reflective material 6 having conventional grain size into the fluorescent material 1. The majority of the ultraviolet rays are converted into visible rays in the fluorescent material layer 8 separated from the housing 5 while the not-yet converted ultraviolet rays passed through said layer 8 are converted into visible rays in the fluorescent material layer 7 nearer to the housing 5. The ultraviolet rays, which have passed conventionally through the nearer fluorescent material layer 7 while not being converted and absorbed by the housing 5 to cause so-called absorption loss, can be reflected to the remote fluorescent material layer 8 by means of the ultraviolet rays reflective material 2 of small grain size existing with high density in the nearer fluorescent material layer 7. Therefore, the ultraviolet rays are converted again into the visible rays in the remove fluorescent material layer 8 so that the light emission efficiency is improved.
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