Design of an inexpensive integrating sphere laboratory setup for the optical characterization of a light source

Since about five years, Lighting has become a partly required and partly elective course within the Energy program of the Master of Engineering Technology at KU Leuven. While the theoretical part of the course is lectured to the entire audience, an increased emphasis has been placed on an individual evaluation of the students for the laboratory module. In order to admit several students simultaneously to the laboratory, multiple constructions of the same laboratory setup are requested. Therefore, cheap alternatives to the scientific metrology instrumentation, which still guarantee that the students get acquainted with optical metrology techniques and general radiometric and photometric quantities, are needed. In this paper, the design of an inexpensive integrating sphere setup is presented, enabling the optical characterization of light sources. Instead of using an expensive sphere with magnesium oxide or barium sulfate coating, a cheap polystyrene sphere is employed. In combination with a low-cost USB spectroradiometer, the system enables the direct measurement of the spectral radiant power of a light source. In addition, the luminous flux, luminous efficacy, colour coordinates, colour temperature, and colour rendering index can be determined. The equipment used, the experimental procedure, as well as some typical measurement results are presented.