<World>
   <Camera eye="0, 100, 300" look_at="0,0,0" fov="70" />
   <Option max_bounces="int 1" />
   <ShaderGroup>
      param float scale_s 20;
      param float scale_t 20;
      param color Ca 0.1 0.1 0.1;
      param color Cb 0.5 0.5 0.5;
      shader checkerboard tex;
      shader matte layer1;
      connect tex.Cout layer1.Cs;
   </ShaderGroup>
   <Quad corner="-200,0,0" edge_x="400,0,0" edge_y="0,400,0" /> <!-- Back -->
   <Quad corner="-200,0,0" edge_x="0,0,400" edge_y="400,0,0" /> <!-- Botm -->

<!--
   <Sphere center="-60,15,120"        radius="5" />
   <Sphere center="-20,15,120"        radius="5" />
   <Sphere center=" 20,15,120"        radius="5" />
   <Sphere center=" 60,15,120"        radius="5" />
-->

   <ShaderGroup>
      param float exponent 10000;
      param color Cs 0.2 0.2 0.7;
      shader phong layer1;
   </ShaderGroup>
   <Quad corner="-80,70, 20" edge_x="0,-20 ,20" edge_y="160,0,0" />
   <ShaderGroup>
      param float exponent 1000;
      param color Cs 0.2 0.2 0.7;
      shader phong layer1;
   </ShaderGroup>
   <Quad corner="-80,45, 50" edge_x="0,-15 ,20" edge_y="160,0,0" />
   <ShaderGroup>
      param float exponent 100;
      param color Cs 0.2 0.2 0.7;
      shader phong layer1;
   </ShaderGroup>
   <Quad corner="-80,25, 80" edge_x="0,-10 ,20" edge_y="160,0,0" />
   <ShaderGroup>
      param float exponent 10;
      param color Cs 0.2 0.2 0.7;
      shader phong layer1;
   </ShaderGroup>
   <Quad corner="-80,10,110" edge_x="0,-5  ,20" edge_y="160,0,0" />

   <ShaderGroup>float power 2000; shader emitter layer1;</ShaderGroup>
   <Sphere center="-90, 130, 50" radius="1" is_light="yes" /> <!--Lite -->
   <Sphere center="-35, 130, 50" radius="5" is_light="yes" /> <!--Lite -->
   <Sphere center=" 30, 130, 50" radius="10" is_light="yes" /> <!--Lite -->
   <Sphere center=" 90, 130, 50" radius="20" is_light="yes" /> <!--Lite -->
   
</World>
