Hi all,
    I have only been playing with POVRay for about a week so am very new. I
noticed in one of the examples a lightbulb was created but it had a
"frosted" bulb. I would like to create a clear bulb so you can see the
filament burning. The bulb was easy enough but I am having some trouble with
the filament. So far I have tried using the looks_like a cylinder on a point
light_source. The cylinder encloses the point of the light source.
Regardless of what I do to the cylinder texture it always looks black. Can
this approach going to give me the desired result? I have seen other
postings that talk about "media" and "glow", should I be using one of these
instead? I haven't gotten that far through the tutorial yet. Any advice is
welcome, thanks in advance.
Rod.

PS here is the light source code as it stands now -
  light_source {
    <0,0,0>
    colour White
    looks_like {
      cylinder {
        <-.15,0,0>, <.15,0,0>, .01
        texture {Glossy}
      }
    }
  }

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I was shocked to hear Rod Reed say:

>The cylinder encloses the point of the light source.
>Regardless of what I do to the cylinder texture it always looks black. Can
>this approach going to give me the desired result? I have seen other
>postings that talk about "media" and "glow", should I be using one of these
>instead? I haven't gotten that far through the tutorial yet. Any advice is
>welcome, thanks in advance.
>Rod.
>
>PS here is the light source code as it stands now -
>  light_source {
>    <0,0,0>
>    colour White
>    looks_like {
>      cylinder {
>        <-.15,0,0>, <.15,0,0>, .01
>        texture {Glossy}
>      }
>    }
>  }
>
>

I've never done this specifically, but I had a similar problem when
looks_like was added.

The problem here is actually mental.  You're thinking that your light
source should look like the cylinder AND glow.  It won't just by
specifying looks_like.  Remember that a light source isn't visible by
itself, so what you get is what looks like a normal cylinder that
casts light, but doesn't glow.  You will need to experiment around
with a fairly hihg ambient on the cylinder to get it too look right,
then try some media effects inside the bulb portion to add that 'glow
effect' to the filament.

- Tim

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In article <3d50f8a6@news.povray.org>, "Rod Reed" <rod### [at] bigpondcom> 
wrote:

>     I have only been playing with POVRay for about a week so am very new. I
> noticed in one of the examples a lightbulb was created but it had a
> "frosted" bulb. I would like to create a clear bulb so you can see the
> filament burning. The bulb was easy enough but I am having some trouble with
> the filament. So far I have tried using the looks_like a cylinder on a point
> light_source. The cylinder encloses the point of the light source.
> Regardless of what I do to the cylinder texture it always looks black. Can
> this approach going to give me the desired result? I have seen other
> postings that talk about "media" and "glow", should I be using one of these
> instead? I haven't gotten that far through the tutorial yet. Any advice is
> welcome, thanks in advance.

The filament texture looks black because you specified a black texture. 
"Glossy" is a finish with some highlights and reflection, neither of 
which would be very visible on a glowing filament, and you didn't 
specify a pigment, so it used the default black pigment.
What you want to do is specify a white pigment for your texture and an 
ambient value of 1 in the finish.

This will make your filament brightly lit, but if you look at a glowing 
filament in real life you will see a halo around it from scattering in 
the air between you and the filament and in the eye. This is what the 
talk of media or glow is about.

-- 
Christopher James Huff <chr### [at] maccom>
POV-Ray TAG e-mail: chr### [at] tagpovrayorg
TAG web site: http://tag.povray.org/

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> The filament texture looks black because you specified a black texture.
> "Glossy" is a finish with some highlights and reflection, neither of
> which would be very visible on a glowing filament, and you didn't
> specify a pigment, so it used the default black pigment.
> What you want to do is specify a white pigment for your texture and an
> ambient value of 1 in the finish.
>
> This will make your filament brightly lit, but if you look at a glowing
> filament in real life you will see a halo around it from scattering in
> the air between you and the filament and in the eye. This is what the
> talk of media or glow is about.

Thanks Chris,
  Between yourself and Chris' response I have solved the black cylinder
problem and realise I need to keep working through the tutorial to get a
more realistic look. I was being mislead by the looks_like command, taking
it at face value in expecting the light source to look like the object. As
for the texture, I realise now that it did not include a pigment, it was my
umpteenth attempt at getting the texture right with what I had read about at
that time, I was getting a little frustrated 8).

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>
> I've never done this specifically, but I had a similar problem when
> looks_like was added.
>
> The problem here is actually mental.  You're thinking that your light
> source should look like the cylinder AND glow.  It won't just by
> specifying looks_like.  Remember that a light source isn't visible by
> itself, so what you get is what looks like a normal cylinder that
> casts light, but doesn't glow.  You will need to experiment around
> with a fairly hihg ambient on the cylinder to get it too look right,
> then try some media effects inside the bulb portion to add that 'glow
> effect' to the filament.
>
> - Tim

Thanks Tim,
 You were right about the problem, I was taking looks_like to mean it would
look like the object. Pretty silly assumption when it comes to computer
programming :-). You're advice on ambient has worked nicely after changing
the pigment back to white, thanks. I think it was black before when I had
white pigment because the outside of the cylinder had no incident light
since the light source was shining from inside the cylinder, maybe anyway.
Rod
PS sorry about the reply to you directly, hit the wrong button on the tool
bar,  I hope it's not a problem.

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I was shocked to hear Rod Reed say:
>PS sorry about the reply to you directly, hit the wrong button on the tool
>bar,  I hope it's not a problem.

not a problem

- Tim

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