Illuminating device and projection display device using the same

A projection display device comprising:

• an illuminating device;
• a display element that is illuminated with light from the illuminating device;
• and
• a projection optical system that projects image light from the display element,
• wherein the illuminating device includes:
• a light source;
• a light guiding unit where light from the light source is supplied to one end surface, and light incident from the one end surface is propagated inside to exit from the other end surface;
• an illuminating optical system that spatially separates a luminous flux output from the other end surface of the light guiding unit into a plurality of luminous fluxes and that forms, on the display element, an optical image that is formed on the other end surface of the light guiding unit;
• a reflective polarizing plate that is located between the illuminating optical system and the display element and that transmits first polarized light while reflecting second polarized light different in polarized state from the first polarized light toward the illuminating optical system;
• a reflecting element that is disposed at a position where the plurality of luminous fluxes are spatially separated, on an optical path between the first light guiding unit and the reflective polarizing plate and that reflects light reflected by the reflective polarizing plate toward the reflective polarizing plate;
• and
• a phase plate that is located between the reflecting element and the reflective polarizing plate;
• and wherein the reflecting element includes transmission regions through which the plurality of luminous fluxes are transmitted, and a reflecting film that is formed in a region other than the transmission regions to reflect the light from the reflective polarizing plate.