I'm trying to model one of those lights put above paintings: basically, a
flourescent tube inside of a 'c' cross sectioned piece of brass.  My idea
was to use an area light on the x-z plane to simulate this light and then
make it look_like an ambient cylinder.

The problem that I'm running into is that it doesn't look like the area
light is working at all.  I get a single high light in my shiny picture
frame and I'm only getting illumination on the picture from the center of
the bulb.  i.e.
it looks like I'm not doing a point light rather than an area light.  My
light code looks like this:

#local halfw=.5;
#local framewidth=.025;
#local wallthickness=(framewidth*2/25);


light_source { < 0, halfh+framewidth, -framewidth*4>  color Gray50
 area_light x*((2*halfw) - (2*wallthickness)), z*framewidth, 10, 10
        } //light_source


image here: http://homepage.mac.com/sstrange/POV/libraryatnight3.jpg
full code here: http://homepage.mac.com/sstrange/POV/pictureframe.inc

As always, apologies if I'm missing something really, really obvious.

thanks,
Steven

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Area_lights are only used to calculate soft shadows. For
specular highlights, it still is a point-light. To achieve
what you want, you'd have to use an actual array of light-
sources (with toned down RGB, as they will add up
later).

Regards,
Tim

-- 
Tim Nikias v2.0
Homepage: http://www.digitaltwilight.de/no_lights


> I'm trying to model one of those lights put above paintings: basically, a
> flourescent tube inside of a 'c' cross sectioned piece of brass.  My idea
> was to use an area light on the x-z plane to simulate this light and then
> make it look_like an ambient cylinder.
>
> The problem that I'm running into is that it doesn't look like the area
> light is working at all.  I get a single high light in my shiny picture
> frame and I'm only getting illumination on the picture from the center of
> the bulb.  i.e.
> it looks like I'm not doing a point light rather than an area light.  My
> light code looks like this:
>
> #local halfw=.5;
> #local framewidth=.025;
> #local wallthickness=(framewidth*2/25);
>
>
> light_source { < 0, halfh+framewidth, -framewidth*4>  color Gray50
>  area_light x*((2*halfw) - (2*wallthickness)), z*framewidth, 10, 10
>         } //light_source
>
>
> image here: http://homepage.mac.com/sstrange/POV/libraryatnight3.jpg
> full code here: http://homepage.mac.com/sstrange/POV/pictureframe.inc
>
> As always, apologies if I'm missing something really, really obvious.
>
> thanks,
> Steven
>
>


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Thanks Tim, I'd been banging my head against that one for a while now.

many thanks,
-Steven

Tim Nikias v2.0 wrote:
>Area_lights are only used to calculate soft shadows. For
>specular highlights, it still is a point-light. To achieve
>what you want, you'd have to use an actual array of light-
>sources (with toned down RGB, as they will add up
>later).
>
>Regards,
>Tim
>
>Tim Nikias v2.0
>Homepage: http://www.digitaltwilight.de/no_lights
>

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We all do at some point. It's just the problem
of thinking in terms of the algorithms. Specular
is just a "hack" to create highlights, it has nothing
to do with actual lightsources, lightreflection etc.
Arealights are used to soften shadows and one
is easily lead to think that an arealight would
actually cover a certain area.
I think there are some other "side-effects" like that
spread throughout POV-Ray, where one would
like to expect the intuitive result, but get different
ones. It takes time and patience figuring all of them
out.
But eventually, you'll know them all (which isn't
meant to say that I know them all... :-)

Regards,
Tim

-- 
Tim Nikias v2.0
Homepage: http://www.digitaltwilight.de/no_lights


> Thanks Tim, I'd been banging my head against that one for a while now.
>
> many thanks,
> -Steven
>
> Tim Nikias v2.0 wrote:
> >Area_lights are only used to calculate soft shadows. For
> >specular highlights, it still is a point-light. To achieve
> >what you want, you'd have to use an actual array of light-
> >sources (with toned down RGB, as they will add up
> >later).
> >
> >Regards,
> >Tim
> >
>


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You might want to read this:

http://www.students.tut.fi/~warp/povQandT/misconceptions.html#arealightconfusion2

  As a side note, also:

http://www.students.tut.fi/~warp/povQandT/misconceptions.html#arealightconfusion

-- 
plane{-x+y,-1pigment{bozo color_map{[0rgb x][1rgb x+y]}turbulence 1}}
sphere{0,2pigment{rgbt 1}interior{media{emission 1density{spherical
density_map{[0rgb 0][.5rgb<1,.5>][1rgb 1]}turbulence.9}}}scale
<1,1,3>hollow}text{ttf"timrom""Warp".1,0translate<-1,-.1,2>}//  - Warp -

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I've been stumbling through and learning, and the lighting misconsceptions
page was a big help. :)

Using an array of lights (not area lights) gave me almost exactly what I
wanted.
image here: http://homepage.mac.com/sstrange/POV/libraryatnight4.jpg
light source code:
  light_source { < currposition, lightcenterheight + 5*wallthickness,
lightcenterdepth>  color red .05 green .05 blue .05
 jitter
 fade_distance 4  fade_power 2
 }


The problem is that the banded shadows coming off of the side of the lamp
makes it obvious I'm using a bunch of descreet lights.  (specifically 30)
One fix I've considered is to also put an area light in there with
extremely high density of area_light in there also.  Is there a better way?
 Should I just bite the bullet and put enough lights in there that the
banding becomes less obvious?

Thanks again for your help on this.  The image is already many many times
better than when I started.

-Steven

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"oldmicah" <nomail@nomail> wrote in message
news:web.3f160f69231f8c259cfc34200@news.povray.org...
>
> Using an array of lights (not area lights) gave me almost exactly what I
> wanted.
> image here: http://homepage.mac.com/sstrange/POV/libraryatnight4.jpg
> light source code:
>   light_source { < currposition, lightcenterheight + 5*wallthickness,
> lightcenterdepth>  color red .05 green .05 blue .05
>  jitter
>  fade_distance 4  fade_power 2
>  }

Might as well remove the keyword 'jitter' since it only works on area_light.

What you could try using instead is spotlight. That way you can attain soft
edges which should blend together and also help to cut down on render time
(maybe). You might need to arrange each of their point_at vectors in such a
way as to be the most efficient and effective. Of course this means there
will ultimately be a directional lighting from the sign's light, if that's
okay.

Bob H.

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