> Am 10.08.2015 um 09:21 schrieb Anthony D. Baye:
>> In an effort to speed the render of the scene I'm working on, I
>> reduced the
>> radiosity settings to default, but wound up with large patches of pure
>> white
>> with jagged edges.  I managed to fix some of it by increasing the
>> number of
>> pretrace steps, but there are still large ambient areas in the render.
>>
>> Can anybody tell me what causes this, and which settings I might
>> adjust to fix
>> it? I can't find anything about this in the documents or tutorials.

>
> *BUT*
>
> if your issue is isolated bright splotches, then the main problem is
> most certainly entirely different, namely that you have some
> comparatively small but very bright object in your scene. In that case,
> you only have two viable options: Up your radiosity "count" parameter,
> or try to replace that bright object with a conventional point or area
> light source (maybe with a looks_like object).
>

In this case, using importance can help.

Add:
#default{radiosity{importance 0.001}}

or
#declare Average_Count = 75;
#declare High_Count = 160000;
#default{radiosity{importance Average_count/High_Count}}

In the radiosity block, set count to a large value:
count 160000

or
count High_Count // With declared indentifier

In your small and bright object(s), add this:
radiosity{importance 1}

That way, on average, you'll use about 160 samples for most of the 
render, but up to 160000 for those problematic small and bright objects.

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