Hi all.

  First off, I'm new here, so if this request needs to be posted
elsewhere...
please tell me!

  I'm trying to make a fish tank.  And for the lid, I need florescent
bulbs.
However, when I try to use an area light (looks_like cylinder), it shows

the whole cylinder, but the light is only coming from the very beginning
point
of the cylinder.  If anyone has an example out there, I'd GREATLY
appreciate
it.  here's what I have:

#declare Tank_Light_Bulb =
cylinder { <0,0,0>,
               <22,0,0>, .75
               texture { pigment { color White} }
               finish { Luminous }
}

light_source
    {
      <1.5,1,9 >
      color White
      area_light
      <22,0,0>,<0,1,0>
      22,1
      adaptive 1
      jitter
      looks_like { object {Tank_Light_Bulb } }
    }

I just want the whole light bulb to eminate light...and it seems to
just come from the originating point.

any help would be appreciated.

-s0da-
mso### [at] erolscom

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First off,your light should be at the center of the cylinder <11,0,0>
Otherwise the code seems correct. But:
POV's area lights only affect shadows, so the lighting on nearby walls still
looks like that of a point light. Perhaps the best solution would be to
create a string of point lights instead of the area light. They need to be
fairly dense to give soft shadows, but at least the lighting is correct.

Margus

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First off, ...thanks for the suggestion.

But do you mean just declare a bunch of light sources at several points
inside the cylinder?  I understand that the more lights I declare,
the smoother the shadows, but also, to make that many lights,
I'd greatly slow down my render time....

isn't there another way?

Margus Ramst wrote:

> First off,your light should be at the center of the cylinder <11,0,0>
> Otherwise the code seems correct. But:
> POV's area lights only affect shadows, so the lighting on nearby walls still
> looks like that of a point light. Perhaps the best solution would be to
> create a string of point lights instead of the area light. They need to be
> fairly dense to give soft shadows, but at least the lighting is correct.
>
> Margus

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Not really. This is a well known difficulty with area_light being not
truly "area". Most people seem to go for a high 'ambient' in the object
to hide the fact (low diffuse too). A very small 'scale' 'normal' will
help spread the point out as well (must have some specular or phong in
there too).
Everythings a work-around far as I know. The multiple lights might be
too slow, true. But if you try that best thing for smooth shadows would
be a wide 'spotlight' 'tightness 1', just not easy to use for such due
to 'point_at'.


Michael Soda wrote:
> I understand that the more lights I declare,
> the smoother the shadows, but also, to make that many lights,
> I'd greatly slow down my render time....
> 
> isn't there another way?

-- 
 omniVERSE: beyond the universe
  http://members.aol.com/inversez/homepage.htm
 mailto:inv### [at] aolcom?Subject=PoV-News

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Michael Soda wrote:
> 
> First off, ...thanks for the suggestion.
> 
> But do you mean just declare a bunch of light sources at several points
> inside the cylinder?  I understand that the more lights I declare,
> the smoother the shadows, but also, to make that many lights,
> I'd greatly slow down my render time....
> 
> isn't there another way?

 One thing that you might try is to use a cylindrical light source
outside the tube itself (check the docs for syntax) and then use a
normal white pigment on the florescent tube with a high ambient value.
A value over one is legal, I sometimes go to 10, and will add white
color to the scene. This combination I feel will give the illumination
that you are looking for and also that white color that florescent
lights are commonly known for. Or you might try the cylindrical light
source inside the tube to see what happens. Use transmit instead of
filter to get the light out or you will lose both intensity as well
as the white color of the tube.

-- 
Ken Tyler

mailto://tylereng@pacbell.net

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Michael Soda wrote:
> 
> Hi all.
> 
>   First off, I'm new here, so if this request needs to be posted
> elsewhere...
> please tell me!
> 
>   I'm trying to make a fish tank.  And for the lid, I need florescent
> bulbs.
> However, when I try to use an area light (looks_like cylinder), it shows
> 
> the whole cylinder, but the light is only coming from the very beginning
> point
> any help would be appreciated.
> 
> -s0da-
> mso### [at] erolscom

 Take the time to read the VFAQ. It answers this question and many more
that are very frequently asked here in the groups. You will find answers
to questions that you didn't know you had yet but wish you had been smart
enough to ask. :)

http://www.students.tut.fi/~warp/povVFAQ.html


-- 
Ken Tyler

mailto://tylereng@pacbell.net

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Looking at your code I see you already have a 22x1 area light. Unless your
light is very long, 22 point lights should do just fine. That is not much
and render time should remain roughly the same. I've had as many as 600
light sources, by the way. Slow, but not outrageously so.
If you like, here's a macro that creates this array (I'm typing it without
POV at hand, I hope I get it right):

//End1 - one end of the string
//End2 - the other end
//Number - number of light_sources

#macro StringLight(End1,End2,Number)
	#local Jump=(End2-End1)/(Number-1);
	#local Count=0;
	#while(Count<=Number)
		light_source{End1+Count*Jump color 1}
		#local Count=Count+1;
	#end
#end

Margus

Michael Soda wrote:
> 
> First off, ...thanks for the suggestion.
> 
> But do you mean just declare a bunch of light sources at several points
> inside the cylinder?  I understand that the more lights I declare,
> the smoother the shadows, but also, to make that many lights,
> I'd greatly slow down my render time....
> 
> isn't there another way?
>

Post a reply to this message

I don't get it. How would you use the cylindrical light? Parallel to the
fluorescent tube? Or pointing where? As far as I can tell a cylindrical
light gives the same illumination as a spotlight, only confined to a
cylinder...

Margus

Ken wrote:
> 
>  One thing that you might try is to use a cylindrical light source
> outside the tube itself (check the docs for syntax) and then use a
> normal white pigment on the florescent tube with a high ambient value.
> A value over one is legal, I sometimes go to 10, and will add white
> color to the scene. This combination I feel will give the illumination
> that you are looking for and also that white color that florescent
> lights are commonly known for. Or you might try the cylindrical light
> source inside the tube to see what happens. Use transmit instead of
> filter to get the light out or you will lose both intensity as well
> as the white color of the tube.
> 
> --
> Ken Tyler
> 
> mailto://tylereng@pacbell.net

Post a reply to this message

Michael Soda <mso### [at] erolscom> wrote:
: isn't there another way?

  Yes, there is: Remove the light source, give a very high ambient value (>=1)
to the cylinder and use radiosity.
  The main problem is to find proper values for the radiostity settings...

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):5;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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That's why I didn't mention it myself. I tried it and got nowhere.

Margus Ramst wrote:
> 
> I don't get it. How would you use the cylindrical light? Parallel to the
> fluorescent tube? Or pointing where? As far as I can tell a cylindrical
> light gives the same illumination as a spotlight, only confined to a
> cylinder...
> 
> Margus
> 
> Ken wrote:
> >
> >  One thing that you might try is to use a cylindrical light source
> > outside the tube itself (check the docs for syntax) and then use a
> > normal white pigment on the florescent tube with a high ambient value.
> > A value over one is legal, I sometimes go to 10, and will add white
> > color to the scene. This combination I feel will give the illumination
> > that you are looking for and also that white color that florescent
> > lights are commonly known for. Or you might try the cylindrical light
> > source inside the tube to see what happens. Use transmit instead of
> > filter to get the light out or you will lose both intensity as well
> > as the white color of the tube.
> >
> > --
> > Ken Tyler
> >
> > mailto://tylereng@pacbell.net

-- 
 omniVERSE: beyond the universe
  http://members.aol.com/inversez/homepage.htm
 mailto:inv### [at] aolcom?Subject=PoV-News

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