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Metrics for daylight calculations (research report) (2015) (pdf)
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Metrics for daylight calculations (research report) (2015) (pdf)

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This report forms the final output of the BRE Trust project 210-14-RM ‘Assessing new metrics for daylighting’ and the CIBSE Research Fund project ‘Assessing new methods for daylight prediction’. Accurate daylight calculation methods are important because they enable the designer to predict the lighting environment in buildings, the resulting energy consumption for lighting, and its input into the overall thermal performance of the building.

Two recent key developments have been the introduction of the Lighting Energy Numeric Indicator (LENI) and the use of climate based daylight modelling to obtain a picture of the overall, year round, daylight performance of a space. This report reviews these approaches to ensure that they can be used as the basis for robust, sophisticated daylight design guidance.

The LENI is a method for predicting lighting energy use. It relies on equations given in EN15193 ‘Energy performance of buildings-Energy requirements for lighting’ to predict daylight factors and the resulting lighting use for different control strategies. In this report, calculations from these equations were compared with the results of daylight modelling in example rooms.


1 Introduction

2 Review of daylight metrics
2.1 Daylight factor
2.2 Calculating daylight in EN15193
2.3 Climate based daylight modelling
2.4 Daylight autonomy
2.5 Useful daylight illuminance

3 Calculating electric lighting use in daylit interiors
3.1 General approach
3.2 Photoelectric switching
3.3 Photoelectric dimming 
3.4 Manual control
3.5 Combinations of control types

4 Modelling daylight in example rooms
4.1 Method used
4.2 Large rooms
4.3 Small rooms

5 Assessment of LENI calculation in EN15193

6 Assessment of climate based daylight prediction

7 Conclusions



Appendix A Results of computer modelling
Appendix B Results of LENI calculations
Appendix C Results of detailed daylight metric calculations

Prepared for: BRE Trust and CIBSE
Prepared by: Cosmin Ticleanu; Paul Littlefair; Gareth Howlett
Authorised by: Andy Dengel (Position Head (Environmental Evaluation)