This page will display the simulated daylight illuminance, based on the given weather data, for any occupied day and time throughout the year.

Using the Select Specific Time pull-down menus, the user selects a specific month, day and time of interest – only days that were simulated based on the annual and weekly occupancy schedule will be available for viewing. Pressing the Display Results button will display the daylight illuminance for the selected day and time in the workplane grid. The illuminance values will be color-coded according to where they fall compared to the design illuminance for the space.

The Weather Results fields display relevant weather information from the weather file for the specified day and time. The global illuminance, diffuse illuminance, reported percentage of opaque sky cover (SPOT actually uses a more advanced metric to detect sky cover), dry bulb temperature, relative humidity, and snow depth are displayed. Comparing global illuminance and diffuse illuminance can give a good idea of exactly how much sky cover exists and what it does to the illuminance calculations in the space under these conditions. Partly cloudy conditions can be very difficult to model as a broad cloudy haze has to be modeled rather than the specific cloud patterns that actually exist on partly cloudy days.

The Workplane Illuminance Statistics fields display average, maximum, and minimum illuminance information for the various electric lighting zones.

The plot at the bottom shows daylighting illuminance calculated for a given day and time based on TMY2 or other climate data. A Climate-Based annual simulation method is used based on the IESNA recommended CIE Sky Model and uses the direct illuminance (illuminance from a 5° circumsolar region) and diffuse illuminance (sky illuminance) to weight cloudy and sunny conditions. The method provides annual accuracy similar to the daylight coefficient approaches, more accurate in some cases as it is not subject to the low resolution of the Klems sky patch approaches. Again note that while annual averages with this method will be fairly accurate, specific day illuminances (particularly under partly cloudy skies) are close estimates but will never accurately represent a future partly cloudy sky condition.


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