[Radiance-general] Re: Radiance simulations maintain 200 lux minimum

[Greg Ward]

Hi Caroline,

Thanks for posting your input and images.  The mostly likely cause of 
your problems is that you left rad to set the default value for -av, 
which is based on your exposure.  Since you use the -2 option to pfilt, 
you don't see the effect this exposure setting has on your image, 
therefore you don't realize that it is probably too high.  You need to 
either manually set the -av value in your render= line, or figure out 
what the correct exposure should be for your scene and use that in your 
EXPOSURE= setting.  Then, the light should be better balanced.

A lot of people set -av 0 0 0 as a matter of course in their 
daylighting simulations.  Although such a conservative setting is 
guaranteed to underestimate your lighting levels, it is often better 
than ending up with too much light where it does not belong, like you 
are seeing here.  At least you noticed it!

The Unix version of radiance comes with a script called compamb that 
automatically determines an appropriate ambient value (and exposure) 
given a rad input file.  I don't believe this is included in 
DesktopRadiance, but you can look for it.

Good luck!
-Greg