Weather data

General description

Weather or climate files are textual files that contain data about weather conditions data for specific location for some time period. They contain data such as sky and sun irradiances, temperatures, wind speed etc.

Weather files can contain real data recorded for some time period on a location. Example of such files are Satel-Light weather files. Although these data are recorded and real data, they don't represent typical climate conditions for some location, and aren't a good source for daylighting calculations.

Another format contains weather data which are statistically analyzed and organized as test reference years (TRY) for some location. They represent typical weather conditions, and as such are suitable for daylighting calculations. Typical time step in these files is one hour, and files contain data for one year period. Example of such format is Energy Plus Weather Format (EPW).

Where to find EPW weather data ?

Files for many places on Earth can be found on:

And companies in many countries can provide specific climate files.


SketchUp model location

For daylight calculations, it is important to locate the model correctly. This feature is in the SketchUp menu:
Window-> Model info-> Geo-location


Weather data inside DL-Light extension


Other climatic elements

Direct sun visibility

DL-Light uses the sun visibility criterion of the World Metheorological organization, direct sun is visible on the sky if direct normal irradiance of the sky is above 120 W/m2.

Standard time versus solar time

Solar time is based on Apparent solar time, the standard time is based on Mean solar time. The gap is about a few seconds. For more details, see the Wikipédia page on Solar time.

All extensions use the standard time except for extension Sun Exposure which allows a calculation in solar time in 'single moment' mode. The time is then interpreted as a local solar time independent of longitude and time zone: the sun is south at 12:00.