Various skylight models had been prepared with different geometry and transparence surface characteristics. The efficiency of the built skylights had been determined in the horizontal "reference” plane that is underneath the horizontal uniform square opening of the skylights — this is the same "theoretical” surface, where the skylight is connected to the lighting well of the daylighting system.

Ф *extemal is the luminous flux that would be absorbed by the 6x6cm reference plane without the presence of the built skylight. The external horizontal illumination had been kept at a constant Eexternal = 428 lx value. The illuminance values had been determined in the reference plane with the help of a measuring head in the grid-points of a uniform 1x1cm measurement grid. This 1x1cm measurement grid (x’;y’) had been revolved by 45° compared to the 6x6cm reference plane of the skylight. The measurement grid has i = 1 ^ 7 measurement points in both (x’) and (y’) directions, that is 49 measurement points altogether. The illuminance values E(x’^/j) — measured in the (x’;y’) grid-points — multiplied by the corresponding area of the measurement points A{x’i;y’j_) provides the luminous flux 0{x’j;y’j) absorbed by the reference plane. The rjskyligM efficiency of the investigated skylight had been calculated as the ratio of the 0extema, luminous flux absorbed by the unobstructed horizontal plane and of the 0reference plana luminous flux

absorbed by reference plane beneath the investigated skylight model using the following equation:

The efficiency of the illustrated "Arched-Shed” skylight geometry with transparent, simple glazing is nArchedShed = 0.41. The investigated skylight characteristics and the corresponding efficiency values can be found in the two-pages attachment.