[Radiance-general] gendaylit

[Jan Wienold]

Martin,

two errors in your gendaylit command line:
1. You mixed up direct and diffuse radiation
2. Gendaylit uses the full spectrum irradiation as input! It's the 
default output which is in the visible range. The Perez model (and 
gendaylit) calculates the luminous efficacy (W -> lm) according the 
actual sky state.
How can you measure irradiantion in the visible range only?

Concerning the reliability, I can underline the statement from 
Christoph. Besides these mentioned validations, we did additional 
validations (measurements of direct and diffuse irradiation and 
horizontal and 4 vertical illuminance) years ago with 10sec data for a 
dataset of one year and found a good match between measurements and the 
model.
Of course, for extrem low sun position, the model could have some 
problems - but also the correct measurements of these flat sun positions 
is often critical. And be careful if you have mean values and not actual 
values (e.g. 1 value for an interval of an hour or 15 min)! This can 
lead also to problems at sunset/sunrise!


Jan


-------------------------------------------------------------------
   o -          
  | \            Jan Wienold
                 Fraunhofer Institute for Solar Energy Systems
                 SOLAR BUILDING DESIGN GROUP - DAYLIGHTING
                 Heidenhofstr. 2
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                 Email: jan.wienold@ise.fhg.de
                
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