Fast measurement of chromatic BSDF and its application to LED lighting

Bidirectional scattering distribution function (BSDF) represents the scattered light distribution in forward and backward directions. BSDF is an important function in precise lighting design, because surface scattering is difficult to determine and including it in simulations. However, to measure a whole field BSDF is time consuming, as it can take as long as a day. In this paper, we propose and demonstrate a new way to measure BSDF. We utilize a screen that is illuminated by the scattered light, and a camera that captures the image on the screen. A complex calibration between the grey level of the camera and intensity is performed to make sure the measurement is valid. Through continuously imaging the screen for various scattered light distributions, an image fusion is performed to present the final BSDF. We call this instrument as screen image synthesis (SIS) BSDF meter. In this paper, two generations of SIS BSDF meter was developed, and is shown in details.