## Summary and Future Prospects

If you don’t know anything about computers, just remember that they are machines that do exactly what you tell them but often surprise you in the result. —Richard Dawkins, 1996 9.1 OVERVIEW OF THE MODELING CHAPTERS The models described in the previous chapters were selected because of the fre­quency of their appearance in the literature […]

The International Building Performance Simulation Association is a good resource for past and present efforts regarding daylighting (and building simulation in gen­eral). Its Web site (http://www. ibpsa. org/m_papers. asp, accessed 10 July 2012) provides access to extensive conference proceedings papers addressing daylight modeling and applications to building simulations. 8.6 SUMMARY Given the large, inefficient loads […]

## Computational Example

In the numerical calculation for standard sky type 11 used in Section 8.5.3, the solar elevation angle 90 – 59.4 = 30.6° (0.534 radians). The air mass m for this geometry is m = 1.9645. Assume the global irradiance GHI is 425 Wm-2. Using average luminous efficacy of GHI from Table 8.2 (115 lm/W), GHL […]

## OTHER SKY LUMINANCE DISTRIBUTION MODELS

Many arbitrary sky conditions other than the 15 CIE “standard” conditions occur in nature, so attempts have been made to develop models relating general sky condi­tions to the CIE standard conditions. Examples were developed by Igawa et al. [20] and Darula and Kittler [21]. The approach is generally to relate the ratio of zenith luminance […]

## SKY LUMINANCE MODEL ACCURACY

Lam, Mahdavi, and Pal [18] discussed the accuracy of the CIE and Perez models and three others. They used measured diffuse sky irradiance data to obtain the estimated magnitude of the luminance at the zenith. Their evaluation compared illuminance levels measured inside an actual daylight space and on the roof of the building. The basis […]

## Computational Example

We compute an example for 8 a. m. standard time for May 30 at a location of 30° N, 105° W, at an elevation of 100 m above sea level. Assume the distribution desired is for a white-blue sky with distinct corona. From Table 8.7, the model type selected is 11; the gradation function is […]

## CIE Gradation and Indicatrix Functions

The CIE relative luminance distribution models can easily be implemented in either computer program codes or spreadsheet programs such as Excel®. The model is based on a set of six “gradation” curves, describing the change in luminance as a function of solar altitude or zenith angle and six “indicatrix” functions. Indicatrix functions describe the theoretical […]

## INTERNATIONAL COMMISSION ON ILLUMINATION MODELS

8.5.1 CIE Standard Sky Models The CIE has constructed a set of “standard sky conditions” to provide guidance regarding the distribution of sky “brightness” for “energy conscious window design, daylight calculation methods and computer programs as well as for visual comfort and glare evaluations” [15, p. 359], see also [16]. According to Kittler, Perez, and […]