Indexes used

2.1.1. Coefficient of reduction Lighting index Cm

The solar factor of a glazing — Seq, is defined as the product of the lighting index Cm, which depends on the quality of the solar protection by the coefficient of transmission of the glazing, S which depends essentially on the type of glazing (see Figure 2). The coefficient Cm allows to determine the performance of the solar protection on the glazing. Cm is determined by the fraction between the total solar energy that comes through the glazing with and without the use of solar shadings. This energy includes the diffuse and direct solar radiation. The more Cm is closed to 0, the more the solar protection is effective.

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Figure 2 : Solar radiation through the window and calculation of the solar factor Seq

2.1.2. Daylight autonomy

As it was defined previously, the reference daylight factors used in Europe are not adapted to tropical climates. The use of a parameter such as the daylight autonomy turns out to be more suitable. Indeed, this coefficient quantifies for a typical year, the percentage of time when the required illumination is available in terms of working requirements.

Thanks to combined use of the three softwares previously presented, it is possible to obtain for each study, the daylight autonomy, the illuminance from the point of view of work as well as the lighting index Cn. In terms of outputs, DAYSIM allows to obtain a mapping of the illuminance level in different points as well as the daylight autonomy of the room [9]. The Energy Plus software allows to obtain the solar radiation through the glazing, then allows to determine lighting index [8].