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From: Mike Horvath
Subject: looks_like
Date: 8 Sep 2016 00:54:14
Message: <57d0eef6@news.povray.org>
Is this the correct way to set up a light_source and attached object?

// Sun
light_source
{
	Source_Location
	rgb light_color
	looks_like
	{
		sphere
		{
			Source_Location, Source_Radius
			texture
			{
				pigment {color rgb light_color}
				finish
				{
					emission	1
					ambient		0
					diffuse		0
				}
			}
		}
	}
	parallel
}

Note that the light source and object are both located at 
Source_Location. I'm not sure how to test whether I'm doing it right or 
wrong.

Mike


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From: clipka
Subject: Re: looks_like
Date: 8 Sep 2016 03:57:15
Message: <57d119db$1@news.povray.org>
Am 08.09.2016 um 06:54 schrieb Mike Horvath:
> Is this the correct way to set up a light_source and attached object?

Nope.
A looks_like object needs to be constructed at <0,0,0>, as POV-Ray
automatically adds a translation to the light source's location.

I do agree that this is poorly documented in the official documentation.


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From: Mike Horvath
Subject: Re: looks_like
Date: 8 Sep 2016 04:00:51
Message: <57d11ab3$1@news.povray.org>
On 9/8/2016 3:57 AM, clipka wrote:
> Am 08.09.2016 um 06:54 schrieb Mike Horvath:
>> Is this the correct way to set up a light_source and attached object?
>
> Nope.
> A looks_like object needs to be constructed at <0,0,0>, as POV-Ray
> automatically adds a translation to the light source's location.
>
> I do agree that this is poorly documented in the official documentation.
>

So this is better?


// Sun
light_source
{
	Source_Location
	rgb light_color
	looks_like
	{
		sphere
		{
			<0,0,0>, Source_Radius
			texture
			{
				pigment {color rgb light_color}
				finish
				{
					emission	1
					ambient		0
					diffuse		0
				}
			}
		}
	}
	parallel
}


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From: clipka
Subject: Re: looks_like
Date: 8 Sep 2016 04:09:51
Message: <57d11ccf$1@news.povray.org>
Am 08.09.2016 um 10:00 schrieb Mike Horvath:
> So this is better?

Yup.


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From: And
Subject: Re: looks_like
Date: 12 Sep 2016 03:10:03
Message: <web.57d65443e29f65168ef8a390@news.povray.org>
clipka <ano### [at] anonymousorg> wrote:
> Am 08.09.2016 um 06:54 schrieb Mike Horvath:
> > Is this the correct way to set up a light_source and attached object?
>
> Nope.
> A looks_like object needs to be constructed at <0,0,0>, as POV-Ray
> automatically adds a translation to the light source's location.
>
> I do agree that this is poorly documented in the official documentation.

 !!


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From: And
Subject: Re: looks_like
Date: 12 Sep 2016 03:25:01
Message: <web.57d6580ae29f65168ef8a390@news.povray.org>
Mike Horvath <mik### [at] gmailcom> wrote:
> On 9/8/2016 3:57 AM, clipka wrote:
> > Am 08.09.2016 um 06:54 schrieb Mike Horvath:
> >> Is this the correct way to set up a light_source and attached object?
> >
> > Nope.
> > A looks_like object needs to be constructed at <0,0,0>, as POV-Ray
> > automatically adds a translation to the light source's location.
> >
> > I do agree that this is poorly documented in the official documentation.
> >
>
> So this is better?
>
>
> // Sun
> light_source
> {
>  Source_Location
>  rgb light_color
>  looks_like
>  {
>   sphere
>   {
>    <0,0,0>, Source_Radius
>    texture
>    {
>     pigment {color rgb light_color}
>     finish
>     {
>      emission 1
>      ambient  0
>      diffuse  0
>     }
>    }
>   }
>  }
>  parallel
> }

A more subtle details is that the light_color usually not the same.
the color of POV-Ray light_source describes the color of the illuminated object.
the color of looks_like object describes the color of (sun) itself. The sun
color often much brighter than the object it illuminates.


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From: And
Subject: Re: looks_like
Date: 12 Sep 2016 04:00:00
Message: <web.57d65fffe29f65168ef8a390@news.povray.org>
"And" <49341109@ntnu.edu.tw> wrote:
>
> A more subtle details is that the light_color usually not the same.
> the color of POV-Ray light_source describes the color of the illuminated object.
> the color of looks_like object describes the color of (sun) itself. The sun
> color often much brighter than the object it illuminates.

I show you the calculation:
The angular diameter of the Sun is about 1/2 degree, so the solid angle of it is
about 0.00006 steradian viewed from Earth. If the luminance of the Sun is
sun_color, than the illuminace of the sun light is sun_color*0.00006, then the
luminance of the reflect surface will be sun_color*0.00006*surface_albedo/pi, so
you should set the color of the POVRay's light_source sun_color*0.00006/pi.
On the other hand, if you set the light_source color A, than the looks_like
color will be A*pi/0.00006 ~= A*52333.


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From: Mike Horvath
Subject: Re: looks_like
Date: 12 Sep 2016 08:44:46
Message: <57d6a33e$1@news.povray.org>
On 9/12/2016 3:57 AM, And wrote:
> On the other hand, if you set the light_source color A, than the looks_like
> color will be A*pi/0.00006 ~= A*52333.
>

Is this even possible? Isn't there a limit on how bright you can make 
something?


Mike


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From: clipka
Subject: Re: looks_like
Date: 12 Sep 2016 09:04:27
Message: <57d6a7db$1@news.povray.org>
Am 12.09.2016 um 14:44 schrieb Mike Horvath:
> On 9/12/2016 3:57 AM, And wrote:
>> On the other hand, if you set the light_source color A, than the
>> looks_like
>> color will be A*pi/0.00006 ~= A*52333.
>>
> 
> Is this even possible? Isn't there a limit on how bright you can make
> something?

Yes, absolutely: Brightness values cannot exceed 3.4e+38 ;)


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From: Mike Horvath
Subject: Re: looks_like
Date: 13 Sep 2016 17:15:15
Message: <57d86c63$1@news.povray.org>
On 9/12/2016 3:57 AM, And wrote:
> On the other hand, if you set the light_source color A, than the looks_like
> color will be A*pi/0.00006 ~= A*52333.
>

Do I apply this to the pigment or the finish emission?


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