> background {
>    color rgb < 0.60, 0.70, 0.95 >
> }
> camera {
>    location <0, 15, -60>
>   direction <0, 2,  1>
>    right x*1.33
>   look_at <0,15,0>
> }
> light_source {
>    <0,28,0> // position of a coner of the light plane
>    rgb<1.0,1.0,1.0>
>    area_light <3, 0, 0>, <0, 3, 0>, 2, 2 // light plane's edges; m by n bulbs
>   adaptive 1 // if on, some rays will not be traced
>   jitter // randomization of bulb's positions, emulating fuzzy shadow edges
> }
>

The adaptive feature value is NOT a boolean value but an initial or 
minimal subdivision value.
It's turned ON by the sole presence of the keyword "adaptive" followed 
by some value, even zero.

adaptive 0 will shoot at least 4 rays in a 2 by 2 array, the size of 
your array.
adaptive 1 will attempt to shoot at least 9 rays in a 3 by 3 array, but 
your array, at 2 by 2, is not large enough.
adaptive 2 will attempt to shoot at least 25 rays in a 5 by 5 array
If a dimention for the sublights is to small in any direction to allow 
for the desired minimal subdivision, it won't attempt to subdivide further.
Using an area_light 3*x, 3*y, 2, 2 with adaptive is totaly pointless.

Using this area_light setting is prety fast and gives very smooth results:
area_light 3*x, 3*y, 33 33 adaptive 0
You can go overboard:
area_light 3*x, 3*y, 1025 1025 adaptive 0
whitch is almost as fast and so smooth that jitter not usefull.



Alain

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