A projector comprises a light source, an Ultraviolet/Infrared Radiation (UV/IR) filter, a color wheel and means for guiding the light beam reflected by the color wheel toward directions away from the light source. The light source is for providing a light beam. The UV/IR filter is disposed with a tilt angle ranging from 13 degrees to 30 degrees. The color wheel for receiving the light beam transmits a primary color light beam of the light beam in a predetermined time section, and the other color light beam of the light beam is reflected by the color wheel. The means for guiding the light beam reflected by the color wheel toward directions away from the light source further guide a invisible light beam of the light beam reflected from the UV/IR filter.