[Radiance-general] Radiance and Ecotect

[Nick Doylend]

Can anyone help here?

I'm trying to model daylight factors on the vertical surface of a 10m high
warehouse rack.  The reflectances are fairly low, 0.3 for the rack and 0.6
for the other surfaces.  I've compared daylight factor results from Ecotect
and Radiance and found big differences in the magnitude and range of values
across the surface.  In one case, Ecotect is giving values varying between
about 7.5% and 1%, the corresponding values from Radiance are between about
2.5% and 0.25%.

Ecotect's export to Radiance facility appears to incorrectly set the
transmissivity of the glazing material in the .rad output.  Setting the
glazing transparency (I guess this is the same as tranmsmittance) in Ecotect
to 0.88 and using the 'clean' glass preset I would expect to see
transmissivity values of 0.96 in the .rad file output.  I'm actually getting
values of 0.66.  Even after correcting the .rad file I still find the output
values to be considerably smaller than those from Ecotect.

I'm using the high quality preset for Ecotect's calculation (further
increasing the quality appears to give slightly larger daylight values), and
an 'indirect reflections' value of 5 for Radiance, all other parameters are
the defaults for Ecotect's Radiance interface.

I suppose my real question here is which values should I trust?  Perhaps
neither.

Nick