He folks.

I'm baaaaaack!!!

(Oh, what's that - no one noticed I was gone? *sigh* Oh well...)

Anyway, I've been wondering about something... I love lights on Christmas
trees. And my dad has more sets of lights than you can shake a VERY big
stick at!! I've been thinking about trying to simulate some with POVRay, but
I already know it's not going to be easy. The question is... Why do bright
lights have an "aura" around them? I mean, you can see a fairy lights from
quite a distance, considering how tiny they are. If I try and draw them with
POVRay they'll be smaller than a single pixel... but in the real world they
have a kind of "glare" around them which takes up more space and makes it
easier to see them from a distance (when they're lit!) Is there some
physical explaination for this?

Or do I just need to clean my glasses???

Thanks!
Andrew.

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In article <3e14aaa2@news.povray.org>,
 "Andrew Coppin" <orp### [at] btinternetcom> wrote:

> Anyway, I've been wondering about something... I love lights on Christmas
> trees. And my dad has more sets of lights than you can shake a VERY big
> stick at!! I've been thinking about trying to simulate some with POVRay, but
> I already know it's not going to be easy. The question is... Why do bright
> lights have an "aura" around them? I mean, you can see a fairy lights from
> quite a distance, considering how tiny they are. If I try and draw them with
> POVRay they'll be smaller than a single pixel... but in the real world they
> have a kind of "glare" around them which takes up more space and makes it
> easier to see them from a distance (when they're lit!) Is there some
> physical explaination for this?

No physical explanation at all, it's magic.

Ok, this is mainly caused by scattering in the air and in the eye. Put a 
little scattering media (types 2, 3, or 4) in the scene, and light 
sources will become visible. Or use the glow patch.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

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"Andrew Coppin" <orp### [at] btinternetcom> wrote in message
news:3e14aaa2@news.povray.org...
>
> I'm baaaaaack!!!
>
> (Oh, what's that - no one noticed I was gone? *sigh* Oh well...)

Now that you mention it... yeah, haven't seen you around.

> Anyway, I've been wondering about something... I love lights on Christmas
> trees. And my dad has more sets of lights than you can shake a VERY big
> stick at!! I've been thinking about trying to simulate some with POVRay,
but
> I already know it's not going to be easy. The question is... Why do bright
> lights have an "aura" around them? I mean, you can see a fairy lights from
> quite a distance, considering how tiny they are. If I try and draw them
with
> POVRay they'll be smaller than a single pixel... but in the real world
they
> have a kind of "glare" around them which takes up more space and makes it
> easier to see them from a distance (when they're lit!) Is there some
> physical explaination for this?
>
> Or do I just need to clean my glasses???

I think it has to do with intensity of light. And lens flare; get a little
fogginess on your glasses and you have instant enhancement of size ,even
though dimmer. Eye retinas are much like a CCD (or vice versa) in that the
photons energize the point where the light touches then blooms it outward
from that point. And the lenses of the eyes are never absolutely perfect
either so some distortions occur. Other factors would be the air acting as a
medium to spread the light or any surroundings which reflect the light, as
opposed to being airless and isolated.

When arriving at my sisters house for Christmas just after dark I noticed
her neighbors Christmas lights strung along a white fence and they looked
like lit up colored pingpong balls instead of the usual kind of lights.
Turned out to be the C9 type is all, while my sisters place actually had a
globe-shaped kind strung along the roof and they looked to me like C9's or
C7's until I realized later what they were.

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Wasn't it Andrew Coppin who wrote:
>He folks.
>
>I'm baaaaaack!!!
>
>(Oh, what's that - no one noticed I was gone? *sigh* Oh well...)
>
>Anyway, I've been wondering about something... I love lights on Christmas
>trees. And my dad has more sets of lights than you can shake a VERY big
>stick at!! I've been thinking about trying to simulate some with POVRay, but
>I already know it's not going to be easy. The question is... Why do bright
>lights have an "aura" around them? I mean, you can see a fairy lights from
>quite a distance, considering how tiny they are. If I try and draw them with
>POVRay they'll be smaller than a single pixel... but in the real world they
>have a kind of "glare" around them which takes up more space and makes it
>easier to see them from a distance (when they're lit!) Is there some
>physical explaination for this?

I don't know about real-world physics, but the simple fix is to use the
MegaPOV "glow" feature. 

-- 
Mike Williams
Gentleman of Leisure

Post a reply to this message

> Anyway, I've been wondering about something... I love lights on Christmas
> trees. And my dad has more sets of lights than you can shake a VERY big
> stick at!! I've been thinking about trying to simulate some with POVRay,
but
> I already know it's not going to be easy. The question is... Why do bright
> lights have an "aura" around them? I mean, you can see a fairy lights from
> quite a distance, considering how tiny they are. If I try and draw them
with
> POVRay they'll be smaller than a single pixel... but in the real world
they
> have a kind of "glare" around them which takes up more space and makes it
> easier to see them from a distance (when they're lit!) Is there some
> physical explaination for this?

Scattering media. Light leaving the bulb that's going not-quite-towards your
eye reflects off of air particles. You can try to simulate it with a *very*
low density scattering media (which is basically a simulation for air
particles, or maybe fog). Make sure you don't use scattering type 1; you'll
probably have the best results using type 5 and fiddling with the
eccentricity value. However, it's probably a lot easier to just use a little
emmitting media around the light to create the glow effect.

 - Slime
[ http://www.slimeland.com/ ]

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Thanks everybody. Was just wondering why this effect occurs. I've noticed
that when I blink the patterns of light scattering change, so I'm thinking
maybe it's the film of water on the surface of my eyes that does it...
Whatever it is, you're all quite right - either scattering media or (more
efficiently) emission will sort of simulate it.

While we're on the subject... Why DO cameras get lense flare? Just
curiose...

See ya's around ;-)
Andrew.

PS. My current WIP is a Single Image Picture Sterogram (SIPS). Don't know if
it'll be any good mind you...

Post a reply to this message

In article <3e15ee3a@news.povray.org>,
 "Andrew Coppin" <orp### [at] btinternetcom> wrote:

> Thanks everybody. Was just wondering why this effect occurs. I've noticed
> that when I blink the patterns of light scattering change, so I'm thinking
> maybe it's the film of water on the surface of my eyes that does it...
> Whatever it is, you're all quite right - either scattering media or (more
> efficiently) emission will sort of simulate it.

Part of it is in the eye and on its surface. Part of it is atmospheric: 
things look very different in rain or fog, and distance affects things 
too.


> While we're on the subject... Why DO cameras get lense flare? Just
> curiose...

A similar reason: the surfaces of the lenses reflect as well as refract. 
Light from a very bright source can bounce through the lens system a 
several times before hitting the film. That is why they sometimes form 
lines of dots of changing size.

-- 
Christopher James Huff <cja### [at] earthlinknet>
http://home.earthlink.net/~cjameshuff/
POV-Ray TAG: chr### [at] tagpovrayorg
http://tag.povray.org/

Post a reply to this message

> A similar reason: the surfaces of the lenses reflect as well as refract.
> Light from a very bright source can bounce through the lens system a
> several times before hitting the film. That is why they sometimes form
> lines of dots of changing size.

Thanks for that!
Andrew.

Post a reply to this message

"Andrew Coppin" <orp### [at] btinternetcom> wrote in message
news:3e14aaa2@news.povray.org...
>  I mean, you can see a fairy lights from
> quite a distance, considering how tiny they are. If I try and draw them
with
> POVRay they'll be smaller than a single pixel... but in the real world
they
> have a kind of "glare" around them which takes up more space and makes it
> easier to see them from a distance (when they're lit!) Is there some
> physical explaination for this?


Well, additionaly to all that has already been said, we benefit from a very
detailed simulation system oft named "reality" which is able to sample each
and every ray for every "pixel" on you retina. Hence, you see lights where
POV has a very great probabilty of seeing nothing because no ray hits the
light (not the light_source point, that is invisible - you can only see its
effects on its surronding, firstly the lamp itself (the glass, ...)).

Povingly,

Philippe

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On Thu, 2 Jan 2003 21:09:46 -0000, Andrew Coppin wrote:

> He folks.
> 
> I'm baaaaaack!!!
> 
> (Oh, what's that - no one noticed I was gone? *sigh* Oh well...)
> 
> Anyway, I've been wondering about something... I love lights on Christmas
> trees. And my dad has more sets of lights than you can shake a VERY big
> stick at!! I've been thinking about trying to simulate some with POVRay, but
> I already know it's not going to be easy. The question is... Why do bright
> lights have an "aura" around them? I mean, you can see a fairy lights from
> quite a distance, considering how tiny they are. If I try and draw them with
> POVRay they'll be smaller than a single pixel... but in the real world they
> have a kind of "glare" around them which takes up more space and makes it
> easier to see them from a distance (when they're lit!) Is there some
> physical explaination for this?
> 
> Or do I just need to clean my glasses???
> 
> Thanks!
> Andrew.

I made my own lens flare include file. It points the camera at a mirror 
with reflection 1 and a specular highlight is used to simulate these halos. 
It works fairly well with point lights but it's a pain to use. The basic 
idea is simple and you should be able to do it yourself.

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