Monitoring and Data Regression of a Φ450mm Monodraught Lightpipe

This paper presents monitoring of a Φ450mm elbowed Monodraught lightpipe at a purposely built test shed with a pitched roof. The monitoring includes use of a cubic integrating box (or known as the ‘BRS Integrating Sky Photometer’) to determine the lumen or illuminance output of the lightpipe. The monitoring results are presented in the format of the lumen output and the illuminance ratio of the output to the external horizontal. To assist the analysis of a huge amount of monitoring data, a formula is proposed to correlate the illuminance ratio, horizontal global illuminance, solar altitude and azimuth, the diameter and length of the lightpipe and the specular reflectance. The coefficients of the formula is given by the regression of the monitoring data. The formula ma be used to predict the performance of the lightpipe.