ZEMCH 2019 International Conference Proceedings April.2020 | Page 327
evaluation of the fabrics in the second cell. The order of fabrics was randomized. Two human subjects
were working per session, alternating between the two cells. One session lasted about 40 minutes (10
questionnaires). A maximum of three sessions (10 questionnaires x 2 persons x 3 sessions) was
organized per day.
The questionnaire consisted in nine questions mixing objective and more subjective questions. It
was mainly based on the work done by [7], but adapted to the local situation and completed by two
questions related to glare, yielding useful data for another part of the project. Among the nine questions,
only two have been dealt with in the context of this paper:
Q1 : Which outside objects can you distinguish from the following : street lamp, kiosk, antenna?
Please circle all that apply :
None
Street lamp
kiosk
antenna
Q2 : Observe the target outside the window, and count how many symbols you can clearly
distinguish for each line :
1st line____
2nd line____
3rd line____
4th line____ 5th line____
The street lamp, the kiosk and the antenna referred to in question Q1 are located at short, middle and
long distances, respectively. The target is an eye chart (Snellen chart in this case) with 5 lines, each line
formed by several symbols (optotypes) starting with the larger symbols in line 1 and continuing
with progressively smaller symbols up to line 5.
The human subjects participating in the study are volunteers. Before starting to fill in the
questionnaire they were informed about the aim of the project and the questionnaire, their rights and
the data protection. They signed a consent letter approved by the Scientific Ethics Committee of Social
Sciences, Arts and Humanities of the university. All data was collected anonymously.
3. Results
Figure 2 gives the scores, averaged over all participants, of the answers to the two objective
questions Q.1. and Q.2., for each of the nine fabrics N1 to N9. A good correlation was observed. All
data was collected for sunny days. From the scores obtained for these two questions, a combined score
was calculated by simply summing both individual scores and normalizing the obtained value to a
scale from 0 to 1. Normalized score 0 corresponds to a totally opaque fabric with no visual contact to
the outside while score 1 corresponds to the optimal visual contact observed with the glazing alone
without any fabric. Figure 3 shows the box plot with the combined and normalized score for the visual
contact with the outside for each of the nine fabrics. On each box, the central mark indicates the median,
and the bottom and top edges of the box indicate the 25th and 75th percentiles, respectively. The
minimums and maximums outside the first and third quartiles are depicted with lines (whiskers). The
symbol x represents the average value. The following observations can be made:
The visual contact with the outside is mainly determined by the openness factor of the fabric and
by its color, or more precisely, by its reflectance value.
For the fabrics showing the same openness factor, the visual contact is always the best for the dark
colored fabric (black‐grey) and the worst for the lightest colored fabric (white). The impact of the
color is more pronounced for the fabrics with the two low openness factors 1% (N1 to N3) and 3%
(N4 to N6). Light‐colored fabric exposed to solar radiation, acts as a secondary source of light,
causing distortion of direct vision through the fabric. As illustration, the following average
luminance values were measured for the three fabrics with the same OF=3% under very similar
solar irradiance: 2781 cd/m², 1111 cd/m² and 181 cd/m² for the white (N4), grey‐white (N5) and
black‐grey (N6) fabrics, respectively.
For the fabrics showing the same color, quite logically, the higher the openness factor, the better
the visual contact.
Interestingly, the visual contact with the outside for the dark‐colored fabric with OF = 3% (fabric
N6) is very similar to that of the light‐colored fabrics with OF = 10% (N7 and N8).
Evaluation of The Visual Contact with The Outside through Solar Shading Fabrics
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