Physical Model, Mirror-box Artificial Sky Testing: Sky Vault Illumination
This mode of testing simulates a uniform overcast sky which is comprised exclusively of sky vault influence. The model is placed inside a mirror box artificial sky chamber. Illumination level measurements are taken with sensors on a grid pattern within the model and are compared to a reference value of available illumination measured inside the sky chamber but outside of the model. The resulting comparison value is called the Daylight Factor (DF) and is a measure of what percentage of available overcast sky illumination reaches the interior measurement point. The overcast sky is generally considered the “worst case” test for illumination levels inside a daylit building. The test does not reflect the performance of the design under direct sun or partly cloudy conditions nor does it reveal the optimal performance of daylighting strategies, such as light shelves or coffers, that attempt to reflect and utilize direct beam sunlight. Ground reflectance is considered by using a neutrally toned ground plane or by including any significant nearby ground features. The surrounding above-ground context is not considered due to the use of the mirrors which are designed to create the effect of the model being placed in a space with an unobstructed horizon. The test is considered a static test in that the time of day, month and year are not influential to the generic overcast sky. Observational images from the remote head video camera described in heliodon studies can be captured to accompany the quantitative data.