An illumination system including a first excitation light source, a second excitation light source and a first diffusion element is provided. The first excitation light source emits a first excitation light beam, and the second excitation light source emits a second excitation light beam. The first and second excitation light beams have different colors. The first diffusion element is disposed on transmission paths of the first excitation light beam and the second excitation light beam, and the first diffusion element includes a first diffusion region and a second diffusion region with different diffusion degrees, wherein at least one of the first excitation light beam and the second excitation light beam sequentially passes through the first diffusion region and the second diffusion region. A projection apparatus is also provided. The illumination system of the invention effectively mitigates a speckle phenomenon of the excitation light beams to achieve a better optical efficiency.

The light source device of the projection display apparatus according to the present disclosure includes: solid-state light sources that individually emit blue light, green light, and red light; a plurality of dichroic mirrors that combine the blue light, the green light, and the red light having exited from the solid-state light sources; a first diffusion plate on which the combined light having been combined by the plurality of dichroic mirrors is incident; a dynamic diffusion plate that is disposed at a position at which the combined light having exited from the first diffusion plate converges and starts to diverge.

The light source device of the projection display apparatus according to the present disclosure includes: solid-state light sources that individually emit blue light, green light, and red light; a plurality of dichroic mirrors that combine the blue light, the green light, and the red light having exited from the solid-state light sources; a first diffusion plate on which the combined light having been combined by the plurality of dichroic mirrors is incident; a dynamic diffusion plate that is disposed at a position at which the combined light having exited from the first diffusion plate converges and starts to diverge.

The light source device of the projection display apparatus according to the present disclosure includes: solid-state light sources that individually emit blue light, green light, and red light; a plurality of dichroic mirrors that combine the blue light, the green light, and the red light having exited from the solid-state light sources; a first diffusion plate on which the combined light having been combined by the plurality of dichroic mirrors is incident; a dynamic diffusion plate that is disposed at a position at which the combined light having exited from the first diffusion plate converges and starts to diverge.

The light source device of the projection display apparatus according to the present disclosure includes: solid-state light sources that individually emit blue light, green light, and red light; a plurality of dichroic mirrors that combine the blue light, the green light, and the red light having exited from the solid-state light sources; a first diffusion plate on which the combined light having been combined by the plurality of dichroic mirrors is incident; a dynamic diffusion plate that is disposed at a position at which the combined light having exited from the first diffusion plate converges and starts to diverge.