Effects of a cylindrical cavity on the etendue of a light source

This paper proposes that the cylindrical cavity around a circular light source can decrease the divergence angle without changing the emission energy and source size. This result can provide a way to reduce the etendue of the light source by scrambling the rays inside the cavity with a lossless scattering surface. The experiment demonstrated that the metallic cavity around the surface source reduced the divergence angle. However, the metallic surface also absorbed quite a large portion of the light energy. The Lambertian nature of the sidewall surface changed the directions of the rays into horizontal directions. It increased the number of reflections inside the cavity and amplified the small amount of absorption at a single reflection. This effect of the cavity on the etendue of the light source can contribute to providing more design flexibility in various lighting applications.