A new method for designing, improving, and measuring hollow light guides

Abstract

We developed a hollow light guide (HLG) model which allows to predict the best extractor combination for any given HLG length and for typical constraints like mean illuminance values and uniformity. The HLG prototype we analysed has a diameter of 30 cm, a 16 m length, 3M prismatic structures on the inner walls, curved light-reflecting surfaces with different shapes working as light extractors. It is powered by a projector with a 400W HIT-lamp. Firstly, we characterised extractors by their flux “consumption” and extraction. Then, we developed an analysis software to allow real time acquisition of floor illuminance data by means of a cooled, calibrated photometric CCD camera. We thus modeled the HLG as a lineal system of extractors. To evaluate both output flux and uniformity of the illuminance distribution of an extensive set of solutions, we wrote a Simulation Software Extractor Position (SISEPO). SISEPO was tested to optimise the extractor sequence of the initial HLG and a 15% improvement of the mean floor illuminance was predicted. The corresponding measured values were in good agreement and also the measurements of the luminous intensity distributions of the whole HLG-luminaire (EULUMDATA), carried out in individual segments of one meter length, confirmed the improvement of the light extraction efficiency.