I want to be able to create a general light source whose intensity is based on a
spherical function, one that has more control than a simple spotlight.

When I was modelling my basement a few years ago, I faked it for modelling my
pot lights.  I simply used a point light inside an no_image sphere that was
mapped with my function for tranparency.  The map was based on light cut sheets
for particular bulbs.

I was trying to do something similar again, but I have the problem that my
spheres shadow other lights in the scene.  No_shadow won't help because I need
shadowing to pick up the transparency.  Light groups don't help because they
only affect lighting on the object and not shadowing of global lights.

Any other ideas?

The easiest solution, that doesn't seem to exist, would be to have an option
where light groups also ignore objects from shadowing global lights.

The most flexible solution would be a function based light source, where the
light intensity is derived from a user defined function.  This would give
flexibility to model several types of light sources, multi-directional lights
spotlights with custom falloff functions etc. (they would even be able to model
a regular point light by having a constant function).  Looks like I may have
another source coding item to have a look at some day...

-tgq

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"Trevor G Quayle" <Tin### [at] hotmailcom> wrote:
> I want to be able to create a general light source whose intensity is based on a
> spherical function, one that has more control than a simple spotlight.
>
> When I was modelling my basement a few years ago, I faked it for modelling my
> pot lights.  I simply used a point light inside an no_image sphere that was
> mapped with my function for tranparency.  The map was based on light cut sheets
> for particular bulbs.
>
> I was trying to do something similar again, but I have the problem that my
> spheres shadow other lights in the scene.  No_shadow won't help because I need
> shadowing to pick up the transparency.  Light groups don't help because they
> only affect lighting on the object and not shadowing of global lights.
>
> Any other ideas?
>
> The easiest solution, that doesn't seem to exist, would be to have an option
> where light groups also ignore objects from shadowing global lights.
>
> The most flexible solution would be a function based light source, where the
> light intensity is derived from a user defined function.  This would give
> flexibility to model several types of light sources, multi-directional lights
> spotlights with custom falloff functions etc. (they would even be able to model
> a regular point light by having a constant function).  Looks like I may have
> another source coding item to have a look at some day...

are you thinking IES profiles for povray?  yep, that would be great.

Post a reply to this message

> I want to be able to create a general light source whose intensity is based on a
> spherical function, one that has more control than a simple spotlight.
>
> When I was modelling my basement a few years ago, I faked it for modelling my
> pot lights.  I simply used a point light inside an no_image sphere that was
> mapped with my function for tranparency.  The map was based on light cut sheets
> for particular bulbs.
>
> I was trying to do something similar again, but I have the problem that my
> spheres shadow other lights in the scene.  No_shadow won't help because I need
> shadowing to pick up the transparency.  Light groups don't help because they
> only affect lighting on the object and not shadowing of global lights.
>
> Any other ideas?
>
> The easiest solution, that doesn't seem to exist, would be to have an option
> where light groups also ignore objects from shadowing global lights.
>
> The most flexible solution would be a function based light source, where the
> light intensity is derived from a user defined function.  This would give
> flexibility to model several types of light sources, multi-directional lights
> spotlights with custom falloff functions etc. (they would even be able to model
> a regular point light by having a constant function).  Looks like I may have
> another source coding item to have a look at some day...
>
> -tgq
>
>
>

First, use all the available paramerets for the spot_light.
Experiment also with area_light.
You can use more than one spot_light with different brightness/colour, 
radius, falloff and tightness. The brightness can be negative.

More advanced:
Model some projector complete with reflector and lense. Use photons. Use 
1 point_light or a pair of spot_light: 1 pointing pointing back at the 
reflector and one pointing forward.



Alain

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> First, use all the available paramerets for the spot_light.
> Experiment also with area_light.
> You can use more than one spot_light with different brightness/colour,
> radius, falloff and tightness. The brightness can be negative.

I'm currently trying to fake it somewhat with spotlights, it'll do for now.

>
> More advanced:
> Model some projector complete with reflector and lense. Use photons. Use
> 1 point_light or a pair of spot_light: 1 pointing pointing back at the
> reflector and one pointing forward.
>

While this may be able to work to try to build realistic reflector maps and
such, it becomes horrendous to render with qaulity settings.

-tgq

Post a reply to this message

> are you thinking IES profiles for povray?  yep, that would be great.

That was one idea.  I think it was IES profiles I used for my lighting before
and mapped out manually.  Another idea I was currently using was to try to model
light scattering by placing (fake) mapped light sources in my media.  It would
be nice to have full control over lighting profiles beyond the functioning that
spotlights have.  Basically an idea I'm throwing out there.  I'll likely look
into how to implement if I can get into source code programming.

-tgq

Post a reply to this message

> I was trying to do something similar again, but I have the problem
> that my spheres shadow other lights in the scene.

How large are these spheres? I would have guessed that to
diminish light from a point light the sphere might be made
very small (barring floating point accuracy issues), maybe
up to the point that its shadow for other light sources
is no longer perceptible?

Post a reply to this message

Christian Froeschlin <chr### [at] chrfrde> wrote:
> > I was trying to do something similar again, but I have the problem
> > that my spheres shadow other lights in the scene.
>
> How large are these spheres? I would have guessed that to
> diminish light from a point light the sphere might be made
> very small (barring floating point accuracy issues), maybe
> up to the point that its shadow for other light sources
> is no longer perceptible?

Yes this would work mostly, however there were instances where I want to apply
area light settings to the light as well, and in that case, the sphere needs to
be larger than the light size.

-tgq

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"nemesis" <nam### [at] gmailcom> wrote:
> are you thinking IES profiles for povray?  yep, that would be great.

I agree, IES profiles would be an outstanding addition to the POV toolkit.

There are a huge number of lights already fully profiled and freely available
online, and the IES profiles are just ASCII files. Here's a format description
and sample parser in C, if anyone's feeling ambitious toward that end (it /does/
seem like fun but I don't currently have the time to spare):

http://lumen.iee.put.poznan.pl/kw/iesna.txt

Cheers,
Rob

-------------------------------------------------
www.McGregorFineArt.com

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"Robert McGregor" <rob### [at] mcgregorfineartcom> wrote:
> "nemesis" <nam### [at] gmailcom> wrote:
> > are you thinking IES profiles for povray?  yep, that would be great.
>
> I agree, IES profiles would be an outstanding addition to the POV toolkit.
>
> There are a huge number of lights already fully profiled and freely available
> online, and the IES profiles are just ASCII files. Here's a format description
> and sample parser in C, if anyone's feeling ambitious toward that end (it /does/
> seem like fun but I don't currently have the time to spare):
>
> http://lumen.iee.put.poznan.pl/kw/iesna.txt
>
> Cheers,
> Rob
>
> -------------------------------------------------
> www.McGregorFineArt.com

I manually modified the IES files for my previous use rather than trying to
build a generic parser.

-tgq

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