Out of curiosity, I made a scene to show the array of elementary lights 
in an area_light and found something that I find surprising:
The outermost elements seem to be about half as bright as the rest, and 
the corner ones dimer still at maybe 1 fourth intensity.

I'm wondering if it's intentional or some oversight.

Here my test scene:
#version 3.7;
global_settings {
   assumed_gamma 1
}

plane{-z, -10 pigment{ rgb 1}finish{brilliance 0} }
//brilliance 0 so that the angle of incidence of
//the light have no effect.

disc{0,z,10000,0.03}
#declare W=11;
#declare N=17;
camera{orthographic location 1*z look_at z up W/2+1.2 right W/2+1.2}
light_source{-10*z rgb<1,0,1>*pow(N,2) area_light W*x W*y N N circular }

light_source{-10*z rgb<0,1,0>*pow(N,2) area_light W*x W*y N N }

Alain

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Am 08.03.2013 23:40, schrieb Alain:
> Out of curiosity, I made a scene to show the array of elementary lights
> in an area_light and found something that I find surprising:
> The outermost elements seem to be about half as bright as the rest, and
> the corner ones dimer still at maybe 1 fourth intensity.
>
> I'm wondering if it's intentional or some oversight.
>
> Here my test scene:

Apparently it isn't:

"line 13: Parse Error: Camera location and look_at point must be different."

Also the up & right camera parameters look peculiar in that they're 
scalars rather than vectors.

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Le 2013-03-08 21:40, clipka a écrit :
> Am 08.03.2013 23:40, schrieb Alain:
>> Out of curiosity, I made a scene to show the array of elementary lights
>> in an area_light and found something that I find surprising:
>> The outermost elements seem to be about half as bright as the rest, and
>> the corner ones dimer still at maybe 1 fourth intensity.
>>
>> I'm wondering if it's intentional or some oversight.
>>
>> Here my test scene:
>
> Apparently it isn't:
>
> "line 13: Parse Error: Camera location and look_at point must be
> different."
>
> Also the up & right camera parameters look peculiar in that they're
> scalars rather than vectors.
>

Chould be:
look_at 2*z up (W/2+1.2)*y right (W/2+1.2)*x

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Am 09.03.2013 20:46, schrieb Alain:
> Le 2013-03-08 21:40, clipka a écrit :
>> Am 08.03.2013 23:40, schrieb Alain:
>>> Out of curiosity, I made a scene to show the array of elementary lights
>>> in an area_light and found something that I find surprising:
>>> The outermost elements seem to be about half as bright as the rest, and
>>> the corner ones dimer still at maybe 1 fourth intensity.
>>>
>>> I'm wondering if it's intentional or some oversight.

This is intentional, and especially important for adaptive area lights: 
Think of an NxM area light not as an array of NxM tiles with "lightlets" 
at their centers, but as an array of (N-1)x(M-1) tiles with "lightlets" 
at their corners: Each "lightlet" then represents a quarter of each tile 
that touches it, which adds up to 4/4 tiles for the inner "lightlets", 
but only 2/4 or 1/4 tiles for those at the perimeter.

Thanks for your inquisitiveness nonetheless, as during investigation I 
found a problem with circular area lights, which are not as homogenous 
as they should be (you might already have noticed this, too).

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Le 13-03-10 04:47, clipka a écrit :
> Am 09.03.2013 20:46, schrieb Alain:
>> Le 2013-03-08 21:40, clipka a écrit :
>>> Am 08.03.2013 23:40, schrieb Alain:
>>>> Out of curiosity, I made a scene to show the array of elementary lights
>>>> in an area_light and found something that I find surprising:
>>>> The outermost elements seem to be about half as bright as the rest, and
>>>> the corner ones dimer still at maybe 1 fourth intensity.
>>>>
>>>> I'm wondering if it's intentional or some oversight.
>
> This is intentional, and especially important for adaptive area lights:
> Think of an NxM area light not as an array of NxM tiles with "lightlets"
> at their centers, but as an array of (N-1)x(M-1) tiles with "lightlets"
> at their corners: Each "lightlet" then represents a quarter of each tile
> that touches it, which adds up to 4/4 tiles for the inner "lightlets",
> but only 2/4 or 1/4 tiles for those at the perimeter.
>
> Thanks for your inquisitiveness nonetheless, as during investigation I
> found a problem with circular area lights, which are not as homogenous
> as they should be (you might already have noticed this, too).
>

It also may have a slight side effect of making the edges of the shadow 
slightly smoother in some cases...

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