The light-guiding apparatus has a light tunnel and an ellipsoidal reflector. Light emitted from the light tunnel is reflected and focused on a DMD chip by the ellipsoidal reflector. The light tunnel and a long axis of the ellipsoidal reflector form an angle. The angle and an eccentricity of the ellipsoidal reflector are used to modify the light emitted from the light tunnel. Thus, the light is made to match an incident angle and an effective dimension of a digital micro-mirror device receiving the light.