Investigation on the influence and uncertainty contribution of the photometric center on photogoniometric measurements

How much light an object emits in certain directions is described by its Luminous Intensity Distribution (LID). It results from integrating over the Luminance of all emitting surfaces, thereby implicitly modelling the object as a point source. The point of the object, that best describes it as a point source, is called the Photometric Center. It is the origin of a source coordinate system, that the LID is expressed in. A far field measurement setup defines its own coordinate system, that has to coincide with the source’s coordinate system. If the Photometric Center and machine center are misaligned the LID measurement is distorted. This paper proposes a model for common far field goniometer geometries and sources that allows to quantify the effect the source position has on the resulting LID. Since the photometric center can only be estimated with a limited confidence, it contributes to the uncertainty of the LID measurement. Therefore, Monte Carlo Simulation is utilized to quantify this uncertainty contribution and determine the conditions, where it becomes significant.