Sky models
Customized Illuminance Analysis and Perspective Illuminance Renderings allow you to specify Sky Models and irradiance data.
| Perez All-Weather Sky | The most commonly used model in daylighting simulation applications and the model most analysts use in Radiance. The Perez model yields accurate results for all sky types from clear to fully overcast. It is also the model LEED requires be used for daylighting predictions. |
| CIE: Overcast Sky, Intermediate Sky, Clear Sky, Uniform Sky | Simplified and standardized instances of the Perez model. They provide standard conditions for daylighting applications. If you know what kind of sky you will have, or you're trying to get values for a particular situation (clear or overcast) then it is a good idea to use a CIE model. |
| Daylight Factor Sky | Percentage of natural light falling on surfaces compared to that which would have fallen on a completely unobstructed horizontal surface under same sky conditions. The location or time of day does not matter if you are using a Daylight Factor Sky. Results will be expressed as a percentage. |
If you are unsure of which sky model to use, a good place to start is with the CIE Overcast Sky model. This model will not have the unique characteristics of direct sun, and represents an overcast condition that could happen at any time of day and is a good way to put your design to the test. It is often standard practice to also render using the Perez model at an equinox and the solstices to visualize a range of standard conditions.