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A Study of Performance of Light Pipes Under Cloudy and Sunny Conditions in the UK
L Shao, S B Riffat, W Hicks and I Yohannes
Institute of Building Technology, University of Nottingham, Nottingham NG7 2RD, UK
ABSTRACT
This paper presents results of an experimental study on the performance of a light pipe in winter under the climatic condition of the UK. A light pipe with top dome and light-distribution diffuser was installed in a model-scale building. The specular interior surface of the 330mm diameter light pipe has a minimum reflectance of 95% and the reflectance of the model interior can be changed by adopting white, grey and black surfaces.
The performance of the light pipe was tested in November, which is in the worst season for daylight, and for overcast and sunny conditions. Both the ratio of interior illuminance to outdoor illuminance and the absolute illuminance inside the model were measured. A typical value of illuminance ratio for a white interior was 14% under a cloudy sky and 7% for sunny conditions. The lower value of the latter is probably due to the low altitude of the sun in the month of the experiment. The absolute illuminance measured under the two conditions were 1600 and 2200 lx, respectively. In a zone of 3¥3m fitted with the same light pipe, the illuminance would be reduced to 100-140 lx. This may still represent a potential energy saving of 30% and the value will increase significantly towards the summer months.
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