Usability of Digital Cameras for Verifying Physically Based ...

Figure 15: Six scatterplots that compare the predicted and the measured illuminances
for each photocell [Mar99].
ena such as small bright clouds, fast moving patchy clouds, rain, snow or heavy
showers could have biased the model. Radiance was therefore capable of reli-
ably predicting the illuminance inside a building for a wide range of sky types –
especially overcast skies – but results that were generated when the circumsolar
region was visible from the point of calculation were considered to be potentially
inaccurate.
The PhD of Mardaljevic also contains an evaluation of existing skylight mod-
els (e.g. the CIE models and the Perez model [PSM93]) and a description of how
Radiance can be used to predict the daylight factor, which describes the ratio
of the internal illuminance at a point to the global horizontal illuminance under
overcast sky conditions and which is commonly used by architects and design
consultants to evaluate the lighting situation inside a building.
2.2.8 Model of the Atrium at the University of Aizu
Two years later, Drago and Myszkowski [DM01] used a photometer (more pre-
cisely a luxmeter, see photometer in appendix B.2) to acquire data about a real
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