Scale models represent a standard method for the assessment of daylighting performance in buildings. Recent studies however pointed out their general tendency to overestimate work plane illuminances and daylight factors. The cause of this inaccuracy between real buildings and scale models performance is due to several sources of experimental errors, such as modelling of building details, surfaces reflectance, glazing transmittance, as well as photometers features. To analyse the principal sources of errors, the comparison of a 1:1 daylighting test module and its 1:10 scale model, placed within identical outdoor conditions, were undertaken. Several scale model parameters were modified in order to determine their impact on the performance assessment, comprising the accurate mocking-up of surfaces reflectance, the model outdoor location, as well as the photometric sensors properties. This experimental study showed that large ranges of discrepancies between daylighting performance figures assessed in both ways can occur, some of them being even caused by slight differences of surfaces reflectance and photometers cosine responses. These discrepancies can be curbed down to a 20% relative divergence, providing that enough time and effort is spent to mock-up the geometrical and photometrical features of the real building.
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