| 摘要 |
PROBLEM TO BE SOLVED: To provide an excellent luminous intensity distribution property without necessitating high manufacturing technique as compared to the conventional technique. SOLUTION: This illuminating optical system 30 is provided with a plano-convex optical element 31 as a whole and two plano-convex lenses 32, 33 in the order from exiting end side of a light guide LG. The optical element 31 has a function of totally reflecting the incident light at the boundary surface 34 between a core 31A and a clad 31B owing to the difference of refractive index. All of respective optical elements of the illuminating optical system 30 are plano-convex, thereby, the surface to be subjected to spherical working is reduced and the fabrication is made easy without necessitating higher working technique than the conventional one. In addition, the optical element 31 having the reflection function of light is constituted so as to satisfy a conditional expression by which the total reflection at a projecting surface of the optical element 31 is prevented and, therefore, much of the light emitted from the light guide LG is efficiently used as illuminating light.
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