Radiance simulations maintain 200 lux minimum?

I have been running several simulations in Radiance
for Winter and Summer solstice at Toronto latitudes.
For noon hour simulations the results are quite
believable along perimeter areas. I have noticed
however, that no matter what changes I make to my
model, the lowest illuminance reading I can generate
anywhere inside a daylit room is between 150 and 200
lux. For afternoon models where the sun is at a
low-angle, the core areas of my models should be below
50 lux (from in-situ light measurements). I understand
Radiance has trouble with low-angle sun simulations.
But when I look at my noon hour models (sun very
high), I notice that my core readings are also all
around 200 lux...seemingly unable to drop below 200
lux. My false colour plots do show minimum extrema
lower than 200 lux, and areas in direct shadow, are
shown more blue (closer to 50 lux on my scale). From
in-situ measurements at desk height, though, it would
seem that the drop off of illuminance levels from the
perimeter to the core of a room is not adequately
represented in my Radiance models. Can anyone offer a
suggestion why my illuminance values, for the most
part, bottom out at 200 lux?



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