Model Measurements in the Artificial Sky

Figure 4: Artificial Sky at the T. U.B.

Figure 5: Cross-Section of the Artificial Sky

The most convenient, reliable and precise solution to describe and follow the illuminance distribution and efficiency of the skylight is to perform scaled model measurements in the artificial sky. The main advantage of these physical model measurement it is possible to follow and analyse all the necessary and investigated material and geometry properties and characteristics — even without knowing the exact mathematical and physical background of the events. In case of the artificial sky the Input can be precisely determined — since any standard CIE sky condition can be set-up. With the help of the scaled, physical model of the daylighting system — the Output can also be measured enabling to analyse, compare and evaluate all the investigated illumination characteristics of actual skylight. The accuracy of this method meets all practical requirements. The sky itself is a 6 m diameter hemisphere, illuminated around its parameter under its horizontal plane. All required standard sky conditions — i. e. CIE Overcast Sky — can be achieved and maintained throughout the measurements. The daylighting model can be placed in the middle of the sky, and inside the model all the illumination values can be measured and the efficiency of the system can be precisely analyzed.

Existing calculation method

to determine light distribution and illuminance efficiency

1.

2.

3.

4.

5.

6.

Transmis­sion of trans­parent structures

Clear or diffused transpa­rent

structures

Obstruction of trans­parent structures

Reflection of trans­parent structures

Shiny or matte light — guiding surfaces

Geometry of skylight

I. Grunn Method

Yes

No

No

No

No

Partly

II. Daniluk Method

Yes

No

Yes

Yes

No

Partly

III. C. I.E.16. Pub­lication, "Skylights”

Yes

No

No

No

No

Partly

IV. C. I.E.16. Publ., "Monitor skylights”

Yes

No

No

No

No

Partly

V. C. I.E.16. Publ., "Shed skylights”

Yes

No

No

No

No

Partly

VI. Lumen Micro 7.0 computer software

Yes

Yes

No

No

No

Partly

VII. TTI TS-A5 Dim. "Dome skylights”

Yes

No

No

Yes

No

Partly

VIII. TTI TS-A5 Effi­ciency of skylights

Yes

No

Yes

No

No

Partly

IX. S. Birch, I. Frame, Daylight

Yes

No

No

No

No

Partly

X. B. R. S. Method

Yes

No

No

No

No

Partly

XI. Lightscape computer software

Yes

Yes

No

No

No

Partly

XII. Skylight Dimen­sioning Method

Yes

Yes

Yes

No

No

Partly

Table 1: Existing Daylighting Calculation and Dimensioning Methods

Existing Daylighting Calculation Methods

The table above (Table 1.) indicates some of the existing investigating methods, and it also lists the properties, taken into consideration to determine the illuminance distribution in the space bellow. None of the listed existing methods or computer software consider all the properties of the skylights, which are playing an important and basic role in the light distribution and efficiency.

These methods are not able to differentiate between shiny or matte surfaces and they are not able to handle all the geometrical properties of a certain light modulating structure. At the calculation of diffused surfaces the transmission values are taken into consideration on a very base level, because these formulae are not including inclination angles of surfaces, which can play very important and determining role in some case.

These facts are proving that the existing calculation methods are all neglecting some important features, this is leading to the necessity to handle the problem using a new and different system of investigation. The model measurements in the artificial sky are able to provide a more exact and global answer to this question.

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