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/ ]

Post a reply to this message

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

Post a reply to this message

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.

Post a reply to this message

On Fri, 17 Jan 2003 15:51:31 -0500, Greg Edwards wrote:

> 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.

A very slight micro-normal on the mirror with really good antialiasing or 
focal blur might work well with bright ambient objects or media as light 
sources but beware of render times!

Post a reply to this message

>>> 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???

Another part of the explanation is the eyelashes of the observer.  They
catch and redistribute small sources of light a lot more than you might
imagine.  I've seen literature on night-time driving simulators which have
explored these problems.

Post a reply to this message

Hey... now that's something I hadn't thought of...

Thanks!
Andrew

Post a reply to this message