I'm trying to cast a light on a black surface such as

box{ -50, 50 scale x/500 pigment{color Black}}


  light_source {
    30*x, Red
    projected_through { sphere{20*x, 1} }
  }

but shining any light on a black surface and the light will not reflect (that is
it has not effect)

However, I want to have an effect like shining a red light on a white wall where
that light source is the only light scen. (or shining a white light on a red
surface, again the only light source in the scene.) So it will appear that the
surface is black and the light is red.

But I can't do that because I need to create a white object, such as

sphere{10*x,3 pigment{color White}}

However, in order to have that visible I would need to have an additional white
light somewhere in the scene, which would illuminate the true pigment of the
wall I'm trying to make look black.

Any ideas?

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If you want the wall to have any color when illuminated, you need it to have 
a pigment besides black. If you want another object to be illuminated 
without illuminating the wall, you could put it in a light_group.

 - Slime
 [ http://www.slimeland.com/ ]

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Woody <nomail@nomail> wrote:
> But I can't do that because I need to create a white object, such as

> sphere{10*x,3 pigment{color White}}

> However, in order to have that visible I would need to have an additional white
> light somewhere in the scene

  No you don't. You just have to set finish { ambient 1 } to that sphere.

-- 
                                                          - Warp

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"Woody" <nomail@nomail> wrote in message 
news:web.486afea135de7638f45a716c0@news.povray.org...
> I'm trying to cast a light on a black surface such as
> ...
> But I can't do that because I need to create a white object, such as
>
> sphere{10*x,3 pigment{color White}}
>
> However, in order to have that visible I would need to have an additional 
> white
> light somewhere in the scene, which would illuminate the true pigment of 
> the
> wall I'm trying to make look black.
>
> Any ideas?
>

A third idea is to illuminate the white object with a directional light (a 
spotlight), so that each object has its own light.
For the 'black' object you could then make it white or grey with 'finish 
{ambient 0}', so that only the illuminated bit showed up.

Regards,
Chris B.

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Add a normal to a black texture, then
there will be some highlights from a flat
surface...

   texture {
      pigment {
         Gray05
      }
      normal {
         granite
         scale 0.005
      }
      finish {
         specular 0.3
         roughness 0.02
      }
   }

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Woody nous illumina en ce 2008-07-02 00:05 -->
> I'm trying to cast a light on a black surface such as
> 
> box{ -50, 50 scale x/500 pigment{color Black}}
> 
> 
>   light_source {
>     30*x, Red
>     projected_through { sphere{20*x, 1} }
>   }
> 
> but shining any light on a black surface and the light will not reflect (that is
> it has not effect)
> 
> However, I want to have an effect like shining a red light on a white wall where
> that light source is the only light scen. (or shining a white light on a red
> surface, again the only light source in the scene.) So it will appear that the
> surface is black and the light is red.
> 
> But I can't do that because I need to create a white object, such as
> 
> sphere{10*x,3 pigment{color White}}
> 
> However, in order to have that visible I would need to have an additional white
> light somewhere in the scene, which would illuminate the true pigment of the
> wall I'm trying to make look black.
> 
> Any ideas?
> 
> 
> 
> 
There is almost no "true" black in the real world. Replace your black with a 
very dark gray, like Gray05 or rgb 0.02.
You can use a second, shadowless, light placed behind the black object or add 
"no_shadow" to that wall.
You can use a very tight spotlight.
You can put your object and a light in a light_group. That light will not shine 
on any object outside it's group.

-- 
Alain
-------------------------------------------------
At twenty years of age the will reigns; at thirty, the wit; and at forty, the 
judgment.
Benjamin Franklin

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