Moreover, the light semi-permeable portion 11 is not restricted in particular in the case in which the light semi-permeable portion 11 has a function for reflecting and diffusing a light and part of lights permeates in the light semi-permeable portion 11 (light permeability: approximately 10 to 50%), and can be made of, for instance, a metal foil such as an aluminum foil, a metal thin film such as