On 23-8-2012 21:27, Nekar Xenos wrote:
> I was trying to figure out how big an area light should be to simulate
> the sun when the light is a lot closer than the sun actually is. Looking
> at a wall about 3m high I noticed the shadow on the ground blurred about
> 3cm. I came to the conclusion that the diameter of my light should be
> about 1% of the distance from the object. To test my theory I looked up
> the diameter of the sun and the distance from the sun to the earth.
> Close enough! The diameter of the sun is 1 391 000 km and the distance
> from the earth to the sun is 149,669,180 km. That's 0.929% :)
>
>

I use the following, originally proposed by Cousin Ricky iirc, which 
seems fairly correct:

#declare SunDis = vlength(SunPosition)*2/215;

   light_source{
     SunPosition
     color SunColor
     area_light
     SunDis*x, SunDis*z,
     5, 5
     adaptive 2
     jitter
     circular
     orient
     parallel
     point_at <0, 0, 0>
   }

Thomas

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