This paper presents initial values of global and diffuse luminous efficacy at Saint-Pierre (Reunion Island). Firstly, data used were measured for a period of 6 months, from February to June 2008. During this period, all defined day-types have been studied (clear, cloudy and intermediate). Generally, the meteorological database of Reunion does not contain information for illuminance values. On the other hand, the local meteorological center has a 60-years-old database for solar irradiance (W.m -2 ). So it is important to determine Luminous Efficacy in order to find illuminance from solar irradiance (or luminance from solar radiance). The measured data were analyzed, and empirical constant models were developed and presented in this paper in order to determine luminous efficacy under different sky conditions. A comparison between these empirical constants (models) and existing models has been made. The method used to define sky conditions (overcast, intermediate and clear) and day-types characterization as well as classification will be presented in this work.
KeywordsGlobal and diffuse luminous efficacy, different sky conditions, solar irradiance, solar illuminance Another reason that prompts us to study these luminous efficacy values is that simulation software for buildings needs specific climatic data, particularly on outdoor illuminance.Hence, luminous efficacy models introduced in the software enables illuminance values simulation using solar irradiance databases.Firstly, empirical (or experimental) constant luminous efficacy (global and diffuse models) for this location (at 21°19'S, 55°28'E) is introduced. Materials, methods and experimental procedures are then presented. Results obtained confirm the accuracy of models.This work was done for a PhD thesis 1 and results obtained are used in CODYRUN 2 simulation software for predicted illuminance values in Reunion Island.
Literature reviewThe luminous efficacy of daylight (in lm/W) is defined as the ratio of daylight illuminance to solar irradiance. With the availability of the measured horizontal and/or vertical solar data, luminous efficacy for horizontal and/or vertical surfaces can be determined respectively. This gives building designers an indication of the relationship between daylight illuminance and solar irradiance. The bibliography is restricted to horizontal luminous efficacy cases only.
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