Climate-based daylight

This page describes the simulation settings and result outputs specific to the Point-in-time Illuminance calculation. For general information about the Daylight tab, including how to define and edit Optical Properties and Measuring Planes, please refer to the generic Daylight tab documentation.

Climate-based daylight simulation uses real weather data to simulate indoor daylight conditions over an entire year. Unlike static methods such as Daylight Factor, climate-based daylight accounts for hourly variations in sky condition and solar position, providing a more accurate and dynamic understanding of daylight availability. It enables the calculation of advanced performance metrics such as Spatial Daylight Autonomy (SDA) and Useful Daylight Illuminance (UDI) which are commonly used in daylight certification standards and green building rating systems.

Calculation settings

Climate-based daylight is calculated for a whole year, with a time-step of 1 hour, using the three-phase method of raytracing lighting simulation software Radiance™.

Type of sky

For climate-based daylight modeling, the Perez sky model is used. This empirical "all-weather" sky model generates hourly sky luminance distributions based on real weather data, which are then processed by Radiance to simulate daylight conditions throughout the year.

Precision

Set the detail level of the Radiance calculation. Click the Precision link to view or edit specific Radiance parameters or to create custom precision settings. For more details see the page Radiance workflow and parameters.

Occupancy source

Some daylight metrics require aggregating simulation results based on the hours a space is occupied. The occupancy source defines when the zones are considered occupied:

• Default: All rooms are considered occupied from 8:00 to 18:00 every day of the year.
• Zones: Occupancy is defined by settings in each zone. The "In use" variable in the Advanced tab of each zone is used, which by default follows the occupant schedules defined within the zone.
• <Simulation name>: Occupancy is determined by the output of a previously run simulation, if applicable.

Controllable shading

Define how internal shading devices (e.g., blinds) are treated during the simulation:

• None drawn: All controllable shades are fully retracted.
• All drawn: All controllable shades are fully deployed.
• According to control signal: Each shade follows the shading control signal logged during the selected simulation.

Simulation with control signal

If "According to control signal" is selected, specify the simulation that provides the shading control data. This simulation must include the "Shading control" output as part of its logged results. Only whole-year simulations are applicable for this setting.

Optical properties

cf. description on the page Daylight tab

Measuring planes

cf. description on the page Daylight tab

Climate-based daylight results

After completion of the climate-based daylight simulation, illuminance data is generated for internal measuring planes and irradiance data for external measuring planes. These raw data values are available for each sensor point on the measuring planes and for every hour of the year and can be visualized and animated within the 3D view, allowing you to examine daylight distribution and performance on both a temporal and spatial basis.

<illustration raw data visualization>

The raw data is then postprocessed into zone-level daylight performance metrics. In the current state, only a predefined set of commonly used metrics is available:

• SDA (Spatial Daylight Autonomy),
• UDI (Useful Daylight Illuminance),
• H_Nutz,a,rel (Relative annual useful illuminance from German standard DIN 5034-3),
• Insolation
   

The transformation from raw simulation results into daylight performance metrics is done by aggregating granular data, first along the temporal axis and then across the considered space.

1. Temporal Aggregation
   For each sensor point, the hourly data is processed over time according to the definition of the metric.

   • For SDA (Spatial Daylight Autonomy), this means computing the percentage of daylight hours (the 4380 brightest hours of the year at the selected location) where illuminance exceeds a threshold (e.g., 300 lux).
   • For UDI (Useful Daylight Illuminance), the percentage of occupied hours during which the illuminance remains within a comfortable range (e.g., 200–2000 lux).
   • For H_Nutz,a,rel the percentage of annual useful illumination to the product of the minimum threshold of illuminance of the zone and occupied hours. The useful illumination is the integral of illuminance from daylight during occupied hours, whereby excesses of the minimum threshold (zone setpoint for minimum daylight - MIN_LIGHT - is applied) do not count.
   • For Insolation, the irradiance data is integrated over time.
      

   This step produces intermediate results that can be visualized as heatmaps and offer a spatial representation of daylight performance across the measuring planes or zones. These heatmaps enable users to view spatial daylight distribution and analyze how daylight availability varies across different areas.

   

2. Spatial Aggregation
   Once temporal aggregation is complete, the results are summarized spatially across each measuring plane or zone:

   • SDA is reported as the percentage of the surface area where the DA exceeds 50%.
   • UDI is reported as the average percentage of occupied hours within the 200–2000 lux range, across all sensor points.
   • H_Nutz,a,rel is reported as the average percentage of the metric across all sensor points.
   • Insolation is reported as the average insolation across the sensor plane.
      

   This step produces scalar daylight metrics that are displayed in the Results table of the Daylight tab. These values provide a compact summary of daylight performance for each zone or measuring plane, and allow for comparative analysis across spaces.

   

   As for other simulations, in the table you can:

   • Select and copy individual cells to paste into other applications,
   • Sort the data by clicking on a column header,
   • Export the entire table to Excel, and
   • Visualize a metric directly on the 3D model by clicking the box icon  in the corresponding column header:
      

   

    

Below is a detailed description of each available daylight metric:

Within the table, you can:

Current limitations

• External shading devices cannot be controlled