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Longyu Guan

Alternative Daylight metrics

With the innovation of technology, both our lit environment and the way people perform indoor tasks have changed. Good visual performance became relatively easy to achieve, and as a result the emphasis of lighting design has moved away from the lighting of working planes. Whilst task illuminance is still in use there is now much more emphasis on the appearance of the room and the people in them. In fact, the term “working plane” has been nominally removed in the European electrical lighting standard. Therefore it is necessary to question the use of working planes in daylight designs.

For many years daylight factor has been the dominant metric used to describe the amount of daylight in a room. However it only considers light falling onto the working plane and thus it may not be the best metric to describe daylight adequacy in modern buildings. A new metric called Mean Indirect Cubic Illuminance (MICI) was proposed and believed to be an improvement over the daylight metrics currently used.

This PhD study tested and compared the performance of the newly proposed MICI with the traditional horizontal illuminance based metrics. Through post-occupancy study and carefully designed controlled experiment, the study concludes that MICI correlates better with people's perception of daylight adequacy.