Illumination system and projection device

A projection device, comprising an illumination system, a light valve, and a projection lens, wherein:

• the illumination system comprises a light source module, a wavelength conversion element, a light path switching module, a first beam splitting element, and a second beam splitting element, wherein:
• the light source module is configured to emit first color light, second color light, and third color light, wherein dominant wavelengths of the first color light, the second color light, and the third color light are different from each other;
• the wavelength conversion element has an O-shaped ring phosphor element;
• the light path switching module is configured to cause the first color light to pass through during a first time interval, and reflect the first color light during a second time interval, wherein the first time interval and the second time interval do not overlap;
• the first beam splitting element is configured to cause the second color light and the third color light to pass through, and reflect the first color light, wherein
• the first color light is transmitted towards a first direction to the light path switching module, and the second color light and the third color light are transmitted towards a second direction to the first beam splitting element;
• after passing through the light path switching module, the first color light irradiates the wavelength conversion element to generate excited light;
• after being reflected by the light path switching module, the first color light is transmitted to the first beam splitting element, and does not irradiate the wavelength conversion element;
• and
• the second beam splitting element is configured to cause the excited light to pass through, and reflect the first color light, the second color light, and the third color light;
• the light valve is disposed on light paths of the first color light, the excited light, the second color light, and the third color light, and is configured to convert the first color light, the excited light, the second color light, and the third color light into an image beam;
• and
• the projection lens is disposed on a light path of the image beam.