Figure 4 presents the results of the lighting index for different d/h ratio and for two different opening azimuths. d represents the length of the overhang and h the height of the window. These values of Cm are also compared to the PERENE requirements.

One can notice that the objectives of PERENE are too difficult to meet. We have assumed that the glazing has a transmittance equal to 1 (the window is opened if it is used in natural ventilation). PERENE requires values of Cm of 0,3 and 0,25 for windows facing North and West respectively.

Values of Cm of 0,3 and 0,5 are respectively demanded for openings oriented East and South. Only a d/h ratio of 1.5 could allow to meet PERENE for an East-oriented window.

To meet acceptable values of Cm, it would be necessary to reduce the transmittance of the glazing, what is not possible if this one is used in natural ventilation. It would be necessary to reconsider the requirements of the PERENE standard, at least for this type of solar shading