While investigating Wikipedia, I came across a fleeting suggestion that 
a material's optical properties are somehow related to its electrical 
and magnetic properties.

Obviously, this seems *highly* implausible, given the abundance of 
materials with similar optical qualities but highly disimilar electrical 
properties, and vice versa. On the other hand... light is supposedly 
related to both electricity and magnetism in some mysterious way. So, in 
principle, it seems as if it *could* be true...

Unfortunately, the article states that the parameters of interest are 
"permitivity" and "permeability". I've checked the articles for both of 
these, and they are entirely beyond my ability to comprehend. (But then, 
so were Wikipedia's articles on DSP and filter design - which actually 
turns out to be quite simple when explained _properly_.)

Does anybody here know anything about this curios idea?

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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Orchid XP v8 wrote:
> Does anybody here know anything about this curios idea?

GIYF?
http://www.newton.dep.anl.gov/askasci/phy05/phy05019.htm
seems to have a pretty good summary.

As the man says, these measurements are an average of what happens when 
photons run into electrons, so it's kind of like "heat" is an average of how 
fast individual atoms are moving that are otherwise unrelated.

-- 
   Darren New, San Diego CA, USA (PST)
   The NFL should go international. I'd pay to
   see the Detroit Lions vs the Roman Catholics.

Post a reply to this message

Darren New wrote:

> GIYF?

Pfff. Yeah, and what do you suggest I search for? "Electricity is 
somehow related top optics"? :-P

> http://www.newton.dep.anl.gov/askasci/phy05/phy05019.htm
> seems to have a pretty good summary.

Mmm, OK. Still not really understanding, but...

> As the man says, these measurements are an average of what happens when 
> photons run into electrons, so it's kind of like "heat" is an average of 
> how fast individual atoms are moving that are otherwise unrelated.

Well, yeah, but "light" as we usually thing of it is a macroscopic 
phenominon too. ;-)

I'm just intrigued by the idea that measuring the electronic properties 
of a substance will tell you all of its optical properties...

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

Post a reply to this message

Orchid XP v8 wrote:
> Pfff. Yeah, and what do you suggest I search for? "Electricity is 
> somehow related top optics"? :-P

I searched on permitivity permeability.

>> http://www.newton.dep.anl.gov/askasci/phy05/phy05019.htm
>> seems to have a pretty good summary.
> 
> Mmm, OK. Still not really understanding, but...

Light reacts primarily with electrons, which absorb it, then later emit it. 
Permittivity is the extent to which charges of different signs go different 
directions. If an electron tends to go left more than right, it builds up a 
charge on the left, which tends to make electrons keep farther away from the 
left, until it's full. Like a capacitor getting full. Clearly, if optics is 
affected by photons interacting with electrons, and there are more electrons 
going one way than the other, you're going to get different optical properties.

Permeability is how easily a magnetic field affects the material. If it 
tends to make the atoms line up, the magnetic field inside the substance 
will get stronger than the magnetic field that's causing things to line up.

The "electric" field is caused by charges, i.e., protons and electrons, 
which interact with photons. The "magnetic" field is caused by photons 
(primarily virtual photons) flooding an area and moving charges around. 
Hence the interactions between them, and the ways in which they affect optics.

> I'm just intrigued by the idea that measuring the electronic properties 
> of a substance will tell you all of its optical properties...

Sure. The light you see is coming from the interactions between photons and 
electrons. *Everything* outside the nucleus except gravity is interaction 
between photons and electrons. All of chemistry, optics, magnetism, 
electricity, heat, biology, etc is the "electronic" properties of 
substances. Measuring the electronic properties of a substance will tell you 
how much weight it will support, what temperature it will melt, how sticky 
it is, and what color it is. :-)

It's hard to measure things that complicated, tho, at that level, because 
the calculations are all infinite sums of hard-to-measure stuff. The nuclear 
interactions appear to follow the same sort of rules, except with 
coefficients on the factors of the infinite sums that converge much more 
slowly, so you have to take many many more terms into account before you can 
come up with a number that's close to what you measure.

-- 
   Darren New, San Diego CA, USA (PST)
   The NFL should go international. I'd pay to
   see the Detroit Lions vs the Roman Catholics.

Post a reply to this message

> While investigating Wikipedia, I came across a fleeting suggestion that a 
> material's optical properties are somehow related to its electrical and 
> magnetic properties.

Of course they are, "optical" properties are just how a material responds to 
a certain frequency band of electro-magnetic waves.  We just think of the 
optical wavelengths differently to the others because that's what our eyes 
respond to.

For example, you know how light "bends" when it enters eg glass, well how 
much it bends is related to the refractive index of the material.  And if 
you know the "electrical" properties you can calculate this refractive index 
exactly (it's the square root of permittivity times permeablility of the 
material).

> Obviously, this seems *highly* implausible, given the abundance of 
> materials with similar optical qualities but highly disimilar electrical 
> properties, and vice versa.

There is no fixed standard rule, but you can see patterns.  For example how 
good electrical conductors also tend to be good thermal conductors, and 
completely opaque to light.  Finding a good conductor that is transparent or 
soft is difficult.  Ditto things that are soft tend to not conduct 
electricity.  An exception is ceramics, which are hard and opaque, but very 
good insulators, that's why they are used on electricity pylons (rubber or 
plastic would suffer much worse weathering).  As always, it's all in the 
atomic level detail, but you can make higher level generalisations.

Post a reply to this message

scott wrote:
>> While investigating Wikipedia, I came across a fleeting suggestion 
>> that a material's optical properties are somehow related to its 
>> electrical and magnetic properties.
> 
> Of course they are, "optical" properties are just how a material 
> responds to a certain frequency band of electro-magnetic waves.  We just 
> think of the optical wavelengths differently to the others because 
> that's what our eyes respond to.

It's more that, in everyday life, there is no way of turning light into 
either electricity or magnetism. I'm sure theoretically it must be 
possible somehow, but it's not something you typically observe.

> For example, you know how light "bends" when it enters eg glass, well 
> how much it bends is related to the refractive index of the material.  
> And if you know the "electrical" properties you can calculate this 
> refractive index exactly (it's the square root of permittivity times 
> permeablility of the material).

So that's the magic relationship? Those two measurements allow you to 
determine the index of refraction?

Presumably knowing the *colour* of an object still requires you to 
compute electron energy band gaps and weird crap like that though?

Post a reply to this message

> It's more that, in everyday life, there is no way of turning light into 
> either electricity

Solar panels.

> So that's the magic relationship? Those two measurements allow you to 
> determine the index of refraction?

Yes, but bear in mind those two properties will likely not be constant over 
frequency (maybe one of them will be, I don't know).

> Presumably knowing the *colour* of an object still requires you to compute 
> electron energy band gaps and weird crap like that though?

Probably, I don't know the details, I just know that for eg car paint there 
is *a lot* of this sort of research to get colour pigments that don't fade 
or change colour after 20 years in the sun.  You certainly need to know your 
chemistry and physics!

Post a reply to this message

>> It's more that, in everyday life, there is no way of turning light 
>> into either electricity
> 
> Solar panels.

And when do you *ever* see those in everyday life? ;-)

>> So that's the magic relationship? Those two measurements allow you to 
>> determine the index of refraction?
> 
> Yes, but bear in mind those two properties will likely not be constant 
> over frequency (maybe one of them will be, I don't know).

Yeah, fair enough. This, presumably, is why we also have the index of 
dispersion! :-D

>> Presumably knowing the *colour* of an object still requires you to 
>> compute electron energy band gaps and weird crap like that though?
> 
> Probably, I don't know the details, I just know that for eg car paint 
> there is *a lot* of this sort of research to get colour pigments that 
> don't fade or change colour after 20 years in the sun.  You certainly 
> need to know your chemistry and physics!

Heh. You know, all I was *actually* trying to find out in the first 
place is whether the reflections on a coloured surface are themselves 
coloured.

It seems I get rather side-tracked. Again.

Post a reply to this message

On Mon, 01 Dec 2008 11:11:43 +0000, Invisible <voi### [at] devnull> wrote:

>>> It's more that, in everyday life, there is no way of turning light 
>>> into either electricity
>> 
>> Solar panels.
>
>And when do you *ever* see those in everyday life? ;-)

http://www.nef.org.uk/renewableenergy/solar.htm

PV applications today are more common place than we might expect. Domestic
burglar alarm systems are now fitted with PV panels to charge the battery for
the system. In Milton Keynes, parking meters are powered by solar panels. ;)
-- 

Regards
     Stephen

Post a reply to this message

>>> Solar panels.
>> And when do you *ever* see those in everyday life? ;-)
> 
> PV applications today are more common place than we might expect. Domestic
> burglar alarm systems are now fitted with PV panels to charge the battery for
> the system. In Milton Keynes, parking meters are powered by solar panels. ;)

LOL! Like I'd know about parking meters - I never go outside, remember? ;-)

(Damnit, suddenly I feel like I'm in a Monty Python sketch. "All right, 
but apart from the sanitation, the medicine, education, wine, public 
order, irrigation, roads, a fresh water system, and public health, what 
have the Romans ever done for us?")

Post a reply to this message

>> Solar panels.
>
> And when do you *ever* see those in everyday life? ;-)

That's just because you live somewhere that is either cloudy or raining the 
whole time :-)  Here they are pretty common, drive through any village and 
you're bound to see at least a few buildings with them on the roof.  Also 
seen a few "solar farms" around, fields literally full of them.

As well as what Stephen said about the parking meters, I've seen them used 
for other road-side things like those warning signs that flash up your 
speed, the little mini weather stations thingies by the side of the 
motorway, etc.

Post a reply to this message

"Invisible" <voi### [at] devnull> wrote in message 
news:4933c66f$1@news.povray.org...
>>> It's more that, in everyday life, there is no way of turning light into 
>>> either electricity
>>
>> Solar panels.
>
> And when do you *ever* see those in everyday life? ;-)

Come to Joburg.
We've got a number of places where solar panels and batteries are used to 
power lit billboards. There are plans to put solar panels at every set of 
traffic lights so that they work even in a power cut.

Post a reply to this message

On Mon, 01 Dec 2008 11:52:29 +0000, Invisible <voi### [at] devnull> wrote:

>>>> Solar panels.
>>> And when do you *ever* see those in everyday life? ;-)
>> 
>> PV applications today are more common place than we might expect. Domestic
>> burglar alarm systems are now fitted with PV panels to charge the battery for
>> the system. In Milton Keynes, parking meters are powered by solar panels. ;)
>
>LOL! Like I'd know about parking meters - I never go outside, remember? ;-)
>

You've got a car, you go to work, the town centre, shops, church (for the organ
playing). No excuses, please :)

>(Damnit, suddenly I feel like I'm in a Monty Python sketch. "All right, 
>but apart from the sanitation, the medicine, education, wine, public 
>order, irrigation, roads, a fresh water system, and public health, what 
>have the Romans ever done for us?")

Solar clocks!
-- 

Regards
     Stephen

Post a reply to this message

>> LOL! Like I'd know about parking meters - I never go outside, remember? ;-)
> 
> You've got a car, you go to work, the town centre, shops, church (for the organ
> playing). No excuses, please :)

What makes you think I go to shops or the town center? :-P

My place of work is a farmer's field, and that church is in a small 
village several miles outside MK.

>> (Damnit, suddenly I feel like I'm in a Monty Python sketch. "All right, 
>> but apart from the sanitation, the medicine, education, wine, public 
>> order, irrigation, roads, a fresh water system, and public health, what 
>> have the Romans ever done for us?")
> 
> Solar clocks!

LOL!

Post a reply to this message

On Mon, 01 Dec 2008 14:10:59 +0000, Invisible <voi### [at] devnull> wrote:

>
>What makes you think I go to shops or the town center? :-P

To get away!
-- 

Regards
     Stephen

Post a reply to this message

Invisible wrote:
> It's more that, in everyday life, there is no way of turning light into 
> either electricity or magnetism. I'm sure theoretically it must be 
> possible somehow, but it's not something you typically observe.

Solar panels. Infrared remote control receivers (i.e., photodiodes). Optical 
sensors on doors.

> Presumably knowing the *colour* of an object still requires you to 
> compute electron energy band gaps and weird crap like that though?

Yes.

-- 
   Darren New, San Diego CA, USA (PST)
   The NFL should go international. I'd pay to
   see the Detroit Lions vs the Roman Catholics.

Post a reply to this message

Invisible wrote:
> Heh. You know, all I was *actually* trying to find out in the first 
> place is whether the reflections on a coloured surface are themselves 
> coloured.

This is just something I ran across somewhere without actually researching, 
but I understood that the difference between a "metallic" reflection and a 
"non-metallic" reflection is whether the reflection still has colors. I.e., 
a reflection off a surface that looks metallic will reflect at least some of 
the colors, while a reflection off (say) plastic will be various shades of 
the color of the plastic itself.  (Isn't this what the "metallic" keyword in 
POV-ray does too?)

-- 
   Darren New, San Diego CA, USA (PST)
   The NFL should go international. I'd pay to
   see the Detroit Lions vs the Roman Catholics.

Post a reply to this message

>> Heh. You know, all I was *actually* trying to find out in the first 
>> place is whether the reflections on a coloured surface are themselves 
>> coloured.
> 
> This is just something I ran across somewhere without actually 
> researching, but I understood that the difference between a "metallic" 
> reflection and a "non-metallic" reflection is whether the reflection 
> still has colors. I.e., a reflection off a surface that looks metallic 
> will reflect at least some of the colors, while a reflection off (say) 
> plastic will be various shades of the color of the plastic itself.  
> (Isn't this what the "metallic" keyword in POV-ray does too?)

Actually the "metallic" keyword affects surface hilights only.

Which leads to another question: Do surface hilights really exist? Or 
are they just reflections of the shape of the light source?

Post a reply to this message

On Mon, 01 Dec 2008 12:11:43 +0100, Invisible <voi### [at] devnull> wrote:
>>> It's more that, in everyday life, there is no way of turning light  
>>> into either electricity
>>  Solar panels.
>
> And when do you *ever* see those in everyday life? ;-)

I used to have a solar powered pocket calculator. Worked pretty well  
indoors too.


-- 
FE

Post a reply to this message

>> It's more that, in everyday life, there is no way of turning light 
>> into either electricity or magnetism. I'm sure theoretically it must 
>> be possible somehow, but it's not something you typically observe.
> 
> Solar panels. Infrared remote control receivers (i.e., photodiodes). 
> Optical sensors on doors.

Infrared receivers *respond to* light. They do not actually *transform* 
it into electricity.

>> Presumably knowing the *colour* of an object still requires you to 
>> compute electron energy band gaps and weird crap like that though?
> 
> Yes.

Damn. :-(

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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On Mon, 01 Dec 2008 21:28:51 +0000, Orchid XP v8 <voi### [at] devnull> wrote:

>> Solar panels. Infrared remote control receivers (i.e., photodiodes). 
>> Optical sensors on doors.
>
>Infrared receivers *respond to* light. They do not actually *transform* 
>it into electricity.

They respond to light (IR) by the light energising the base of a transistor the
same way an electric current does. In fact you can make a photo transistor by
opening the can of a metal clad tyranny. 

-- 

Regards
     Stephen

Post a reply to this message

Fredrik Eriksson wrote:
> On Mon, 01 Dec 2008 12:11:43 +0100, Invisible <voi### [at] devnull> wrote:
> I used to have a solar powered pocket calculator. Worked pretty well
> indoors too.

	Many such gadgets do include a battery. My solar powered calculator
would work well in complete darkness. Until the battery ran out (took
about a decade to do so!). Now it works, but needs some light (not much,
though).

-- 
Intaxication: Euphoria at getting a tax refund, which lasts until you
realize it was your money to start with.


                    /\  /\               /\  /
                   /  \/  \ u e e n     /  \/  a w a z
                       >>>>>>mue### [at] nawazorg<<<<<<
                                   anl

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On Tue, 02 Dec 2008 01:02:37 +0100, Mueen Nawaz <m.n### [at] ieeeorg> wrote:
> Fredrik Eriksson wrote:
>> On Mon, 01 Dec 2008 12:11:43 +0100, Invisible <voi### [at] devnull> wrote:
>> I used to have a solar powered pocket calculator. Worked pretty well
>> indoors too.
>
> 	Many such gadgets do include a battery. My solar powered calculator
> would work well in complete darkness. Until the battery ran out (took
> about a decade to do so!). Now it works, but needs some light (not much,
> though).


Not this one. If you held your hand over the solar cells the display would  
blank out right away. I still have a non-solar-powered calculator though  
that runs on its original battery even after twenty or so years. The power  
consumption of such devices is astonishingly low.


-- 
FE

Post a reply to this message

"Fredrik Eriksson" <fe79}--at--{yahoo}--dot--{com> wrote:
> Not this one. If you held your hand over the solar cells the display would
> blank out right away. I still have a non-solar-powered calculator though
> that runs on its original battery even after twenty or so years. The power
> consumption of such devices is astonishingly low.

I remembered if I covered the solar cells for the right brief amount of
time, the number changed in such a way that I think only some bits got
cleared :)

Post a reply to this message

> Which leads to another question: Do surface hilights really exist? Or are 
> they just reflections of the shape of the light source?

They do exist, and they are not just reflections of the shape of the light 
source.  They are due to the geometric structure of the surface on a very 
small scale.  Think about each surface IRL actually having something like a 
normal{bumps scale 0.000001} block and then rendered with perfect 
anti-aliasing... even a point light source will give you a non-zero sized 
highlight.

Diffuse, specular and reflection are all the same thing IRL, it just depends 
on the geometry of the surface.  IIRC some light reflection model used in 3D 
cards (or maybe POV too) is based on theoretical analysis of random surface 
variations.  Something like assuming the surface to be made up of a 
triangle-wave with each peak a random height.  You can calculate the % of 
light reflected in certain directions mathematically and with a few 
simplifications come up with a model for diffuse and specular components.

Post a reply to this message

Darren New wrote:
> 
> Solar panels. Infrared remote control receivers (i.e., photodiodes). 
> Optical sensors on doors.
> 

Don't forget digital camera sensors. DRAM chips, too.

-- 
~Mike

Post a reply to this message

Invisible wrote:
>>> It's more that, in everyday life, there is no way of turning light 
>>> into either electricity
>>
>> Solar panels.
> 
> And when do you *ever* see those in everyday life? ;-)

You have probably seen several solar powered calculators, watches and 
torches.

See:

http://www.amazon.com/Casio-FX-260-Solar-Scientific-Calculator/dp/B00004TVDT
http://www.globalsources.com/manufacturers/Solar-Torch.html
http://www.thesolarcentre.co.uk/catalog/Solar_Watches-27-1.html
http://www.thesolarcentre.co.uk/

-- 
Tor Olav
http://subcube.com

Post a reply to this message

scott wrote:
...
> For example, you know how light "bends" when it enters eg glass, well 
> how much it bends is related to the refractive index of the material.  
> And if you know the "electrical" properties you can calculate this 
> refractive index exactly (it's the square root of permittivity times 
> permeablility of the material).
...

Heh - now you just reminded my of this Google calculator expression:

http://www.google.no/search?q=speed+of+light+times+square+root+of+%28permittivity+of+free+space+times+permeability+of+free+space%29
http://tinyurl.com/5etcgr

-- 
Tor Olav
http://subcube.com

Post a reply to this message

Tor Olav Kristensen wrote:
> Heh - now you just reminded my of this Google calculator expression:
> 
>
http://www.google.no/search?q=speed+of+light+times+square+root+of+%28permittivity+of+free+space+times+permeability+of+free+space%29
> http://tinyurl.com/5etcgr
> 

http://www.google.com/search?q=once+in+a+blue+moon

Post a reply to this message

Nicolas Alvarez wrote:
...
> http://www.google.com/search?q=once+in+a+blue+moon

=)

So we have a blue moon about every 33rd month ?

http://www.google.com/search?q=one+divided+by+once+in+a+blue+moon+in+months

-- 
Tor Olav
http://subcube.com

Post a reply to this message

Nicolas Alvarez wrote:
> http://www.google.com/search?q=once+in+a+blue+moon

And of course don't forget
http://google.com/search?q=the+answer+to+life,+the+universe+and+everything

Post a reply to this message

"Tor Olav Kristensen" <tor### [at] TOBEREMOVEDgmailcom> wrote in message 
news:4935a069@news.povray.org...
>
>
http://www.google.no/search?q=speed+of+light+times+square+root+of+%28permittivity+of+free+space+times+permeability+of+free+space%29
> http://tinyurl.com/5etcgr
>

Someone posted here, once, quite a while back, an absolutly massive google 
calculator query that involved the permeability and permittivity of free 
space, plus a whole bunch more things and gave teh answer in something 
absurd, like nautical miles per half hour. I recall the query taking several 
lines.

Does any one else remember? Does anyone perhaps still have that?

Post a reply to this message

Nicolas Alvarez wrote:
> Nicolas Alvarez wrote:
>> http://www.google.com/search?q=once+in+a+blue+moon
> 
> And of course don't forget
> http://google.com/search?q=the+answer+to+life,+the+universe+and+everything

And some more:

http://www.google.no/search?q=great+gross+fathoms+in+number+of+horns+on+a+unicorn+foot
http://www.google.no/search?q=two+nautical+miles+per+quarter+year+in+furlongs+per+fortnight
http://www.google.no/search?q=two+great+gross+chains+in+bakers+dozen+hands
http://www.google.no/search?q=avogadros+number+half+torr+in+pounds+per+square+parsec
http://www.google.no/search?q=cubic+light+years+in+imperial+dessert+spoons
http://www.google.no/search?q=e+pennyweights+per+american+cup+in+carat+per+hogshead
http://www.google.no/search?q=pi+astronomical+units+per+quarter+barrel+in+cubits+per+firkin

-- 
Tor Olav
http://subcube.com

Post a reply to this message

It can do math with complex numbers too:

http://www.google.no/search?q=e%5E%28i*pi%29%2B1

-- 
Tor Olav
http://subcube.com

Post a reply to this message

Invisible wrote:
>> (Isn't this what the "metallic" keyword in POV-ray does too?)
> 
> Actually the "metallic" keyword affects surface hilights only.

There are two 'metallic' keywords - one for highlights, and one for 
specular reflection.

> Which leads to another question: Do surface hilights really exist? Or 
> are they just reflections of the shape of the light source?

Yes, and yes.

Post a reply to this message

>>> (Isn't this what the "metallic" keyword in POV-ray does too?)
>>
>> Actually the "metallic" keyword affects surface hilights only.
> 
> There are two 'metallic' keywords - one for highlights, and one for 
> specular reflection.

...there are?? o_O

>> Which leads to another question: Do surface hilights really exist? Or 
>> are they just reflections of the shape of the light source?
> 
> Yes, and yes.

Hmm. I see. I think...

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

Post a reply to this message

Orchid XP v8 wrote:
>>>> (Isn't this what the "metallic" keyword in POV-ray does too?)
>>>
>>> Actually the "metallic" keyword affects surface hilights only.
>>
>> There are two 'metallic' keywords - one for highlights, and one for 
>> specular reflection.
> 
> ...there are?? o_O

Metallic in a finish block relates to highlights, metallic in a 
reflection block relates to specular (mirror) reflection. It's in the docs!

Watchit, this is getting dangerously off-off-topic!

>>> Which leads to another question: Do surface hilights really exist? Or 
>>> are they just reflections of the shape of the light source?
>>
>> Yes, and yes.
> 
> Hmm. I see. I think...

They're very blurred reflections of very bright objects - you see 
highlights of anything bright. More unbiased renderers like indigo etc 
don't actually use highlights, you get them for free with the lighting 
model.

:)

Post a reply to this message

Bill Pragnell wrote:

> Metallic in a finish block relates to highlights, metallic in a 
> reflection block relates to specular (mirror) reflection. It's in the docs!

How interesting... I never knew that!

> Watchit, this is getting dangerously off-off-topic!

:-P

>>>> Which leads to another question: Do surface hilights really exist? 
>>>> Or are they just reflections of the shape of the light source?
>>>
>>> Yes, and yes.
>>
>> Hmm. I see. I think...
> 
> They're very blurred reflections of very bright objects - you see 
> highlights of anything bright. More unbiased renderers like indigo etc 
> don't actually use highlights, you get them for free with the lighting 
> model.

Wait - I just said "are they just reflections of the light source".

So are they or aren't they?

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

Post a reply to this message

Orchid XP v8 wrote:
> Wait - I just said "are they just reflections of the light source".
> 
> So are they or aren't they?

In POV-Ray, they are just reflections of the light source. In real life, 
you see highlights for any relatively bright object, because any 
relatively bright object behaves like a light source.

I see highlights on my tea mug that correspond to the TV, several lights 
and the bit of paper next to it on the coffee table. On closer 
inspection, they're all just regular reflections, and everything else in 
the room is insufficiently bright to show up.

If I'm just being confusing, you should menace me with your best baby 
panda impression... :)

Post a reply to this message

Orchid XP v8 wrote:

> 
> Wait - I just said "are they just reflections of the light source".
> 
> So are they or aren't they?
> 

They are, sort of. In the real world, highlights would be caused by very 
fine irregularities on the surface. which will invariably reflect some 
of the light from the light source to your eye. What you see, then is a 
diffused reflection of the object's surroundings. Some of which may 
actually be a light source.

Highlights as POV-Ray defines them is a sort of short cut. Depending on 
rougness, or highlight size, depends on the angles at which the 
highlight can be seen. It's a mathematical shortcut to simulate a 
(slightly) rough surface without needing to use such things as 
micronormals, or shooting thousands of rays from each point of the 
surface. Instead they use a simple formula to get what they need.
-- 
~Mike

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Mike Raiford wrote:

> They are, sort of. In the real world, highlights would be caused by very 
> fine irregularities on the surface. which will invariably reflect some 
> of the light from the light source to your eye. What you see, then is a 
> diffused reflection of the object's surroundings. Some of which may 
> actually be a light source.
> 
> Highlights as POV-Ray defines them is a sort of short cut.

Right. This is basically what I thought. ;-)

Doesn't that mean that, in the real world, the hilights should be the 
shape of whatever luminous object is creating them? (The real world 
doesn't have point-lights.)

-- 
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*

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Orchid XP v8 wrote:
>> Highlights as POV-Ray defines them is a sort of short cut.
> 
> Right. This is basically what I thought. ;-)
> 
> Doesn't that mean that, in the real world, the hilights should be the 
> shape of whatever luminous object is creating them? (The real world 
> doesn't have point-lights.)

Aye. With additional deformation due to the shape of the surface, of course.

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Mike Raiford wrote:
> They are, sort of. In the real world, highlights would be caused by very 
> fine irregularities on the surface. 

You don't even need fine irregularities. Quantum randomness would be enough.

Conductive metal reflects shiney because there's a "layer" of free electrons 
floating between atoms, and they interact with the light in a much 
"smoother" way than electrons interacting with electrons bound to atoms. So 
being conductive is caused by the same thing as being reflectively shiny.

Of course, if the surface isn't smooth to start with, you're unlikely to see 
a mirror-like reflection to start with. But you're going to have a hard time 
polishing untreated wood to a shine no matter how smooth you make it, and if 
you start getting something like fluorescence, you start seeing that 
reflections aren't really "bouncing" light at all, but light that's absorbed 
and re-emitted..

-- 
   Darren New, San Diego CA, USA (PST)
   The NFL should go international. I'd pay to
   see the Detroit Lions vs the Roman Catholics.

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>> Highlights as POV-Ray defines them is a sort of short cut.
>
> Right. This is basically what I thought. ;-)
>
> Doesn't that mean that, in the real world, the hilights should be the 
> shape of whatever luminous object is creating them? (The real world 
> doesn't have point-lights.)

Yes, if your surface was perfectly smooth.  But IRL most surfaces are not, 
they have a roughness even if it is at a very small scale, thus the "normal" 
you use in the reflection equation is perturbed slightly which can make the 
highlight look larger and more blurred than it would due to a straight 
reflection.

http://en.wikipedia.org/wiki/Specular_highlight

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Darren New <dne### [at] sanrrcom> wrote:
> Of course, if the surface isn't smooth to start with, you're unlikely to see
> a mirror-like reflection to start with. But you're going to have a hard time
> polishing untreated wood to a shine no matter how smooth you make it

That's because wood in itself has such an extreme inhomogenity at microscopic
scale.

You can polish stone or plastic though to get mirror-like reflections.
They'll not be as prominent as in metal because they have to compete with
diffuse reflection, but the mirror-like component is still in there.


> and if
> you start getting something like fluorescence, you start seeing that
> reflections aren't really "bouncing" light at all, but light that's absorbed
> and re-emitted..

That's pure nonsense. If you deal with fluorescence you'll see that *all*
re-emitted light is *undirected* (at least with relation to the direction of
the absorbed light).

*Specular* reflections (i.e. the thing we'd normally call reflections - not to
be confused with PoV-ray's shortcut of "specular highlights") are *really*
"bouncing" light; it's the result of the electromagnetic wave (the "probability
wave" of the photon if you want to go Quantum) being unable to fully enter the
medium (speaking of permeability and permittivity), so the light wave (or part
of it) simply reflects, in order to comply with Maxwell's equations.

It can't work with absorption and re-emission - because the "incoming angle =
outgoing angle" law of specular reflection is a result of a light wave's
interference with itself. But as soon as a photon is absorbed by an electron,
the photon's probability wave collapses, so the re-emitted light's probability
wave has no way of interferencing with it, even if the direction of emission
would be in any way related to the absorbed photon.

It also can't work with absorption and re-emission because both are limited to
certain wavelengths for many materials, unless you go high temperature. Yet
specular reflections off most polished materials (except metals) are pure
"white" - even for materials that do show a strong color.

Only *Diffuse* reflections (i.e. the thing we'd normally not call reflections at
all) *may* sometimes be due to absorbed and re-emitted light.

Note however that quite a lot of instances of diffuse reflection are still
"bouncing" light. If you take a heap of fine-grained sugar for example, it the
diffuse white reflection is actually due to a very random sequence of
reflections and refractions at the single sugar crystals. A single "white"
sugar crystal is quite transparent though, so no absorption happening there.
And "brown" sugar gets its color because some of the light traversing the
crystals is absorbed by natural impurities - but there's no re-emission
involved (at least not to any significant degree in the visible spectrum).

You also typically get re-emissions at different (usually longer) wavelengths
than the absorbed photons (if only because of the principle of entropy). UV in,
visible out is a typical thing; or visible in, infrared out, though that's
usually due to thermal emissions. Green in, amber out is a possiblity as well.

In fact, what we'd normally call "diffuse" reflection is typically a combination
of some light "bouncing" at the surface, some light being absorbed by the
medium, some light "bouncing" below the surface ("subsurface scattering"), and
some (though usually not much) light (re-) emitted.

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clipka wrote:
> You can polish stone or plastic though to get mirror-like reflections.

You'll get recognisable reflections. You won't get a reflection like a 
mirror gives. That's more what I meant. You'll get "polished" rather than 
"shiny", if that makes sense.

> That's pure nonsense. If you deal with fluorescence you'll see that *all*
> re-emitted light is *undirected* (at least with relation to the direction of
> the absorbed light).

Of course this is true with flourescence, because you're emitting a 
different frequency than you absorbed. It's not true in general. See, for 
example, a laser, where all re-emitted light is specifically in the same 
direction and phase as the absorbed photon that triggers the re-emission.

> in order to comply with Maxwell's equations.

Maxwell's equations are a statistical summarization of the actual behavior.

> It can't work with absorption and re-emission - because the "incoming angle =
> outgoing angle" law of specular reflection is a result of a light wave's
> interference with itself. 

Sort of. What would keep interference from working between an absorbed 
photon and a re-emitted photon?

> But as soon as a photon is absorbed by an electron,
> the photon's probability wave collapses, 

This is incorrect, as far as I understand it. OK, well, for the kind of 
"absorb" you're talking about, where the photon turns into a higher energy 
band of electron "orbit", that might be right. But not for simple "change of 
direction" kind of absorption.

> so the re-emitted light's probability wave has no way of interferencing with it, 

Also incorrect. You can get interference between two photons that aren't 
even in the same light cone any more.

> It also can't work with absorption and re-emission

Perhaps my reference to florescence has made the rest of my statements mean 
something to you different than what I intended. When I say "absorption and 
re-emission", i'm talking at the level of individual photons interacting 
with individual electrons in a QED sort of way. I'm not talking about 
absorption and then re-emission some (theoretically) measurable time later, 
like you get with fluorescence.

> because both are limited to certain wavelengths for many materials, 

I think we're talking about different types of absorption and re-emission. 
I'm talking individual photons interacting with individual electrons. I.e., 
I'm talking about the scale where it's nonsensical to argue whether it's the 
"same" photon or a "different" photon.

> Note however that quite a lot of instances of diffuse reflection are still
> "bouncing" light. 

Light "bounces" off the electrons of an atom. Whether you want to call it 
"absorb and re-emit" or whether you want to call it "bounce" simply depends 
on whether you want to think of it as the same photon or a different photon, 
which is a question that makes no sense.

> You also typically get re-emissions at different (usually longer) wavelengths
> than the absorbed photons (if only because of the principle of entropy).

Yes. I confused you with my mention of fluorescence. Sorry about that.

-- 
   Darren New, San Diego CA, USA (PST)
   The NFL should go international. I'd pay to
   see the Detroit Lions vs the Roman Catholics.

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Darren New <dne### [at] sanrrcom> wrote:
> clipka wrote:
> Of course this is true with flourescence, because you're emitting a
> different frequency than you absorbed. It's not true in general. See, for
> example, a laser, where all re-emitted light is specifically in the same
> direction and phase as the absorbed photon that triggers the re-emission.

Nay. If a laser would work this way, it wouldn't be a lAser ("Light
*Amplification* by stimulated emission of radiation"). The laser effect is a
totally different story.

In a laser, the lasing medium are "pumped" in some way by an external source;
typically, this is a high-energy (i.e. short-wavelength) radiation source
outside the lasing medium, like an UV lamp. *That* is what the electrons in the
lasing medium actually absorb.

The emission then happens in a totally different, lower-energy spectral band,
and can happen spontaneously; or it can be stimulated by light of that very
frequency and will then have the same direction and phase as the stimulating
photon; but the stimulating photon is *not* absorbed.


> Maxwell's equations are a statistical summarization of the actual behavior.

Nay. They are an *exact* description of the *waveforms* which *determine*
statistical behavior (the "probability wave" of a particle between actual
interactions).


> Sort of. What would keep interference from working between an absorbed
> photon and a re-emitted photon?

The fact that the photon has at last stopped being a wave (having just a certain
*probability* to be somewhere) and started being a particle (actually
interacting *somewhere* particular).

It is also described of the "probability wave" of the photon having "collapsed".

That's the moment where Maxwell can go home, and have a break until another
photon is emitted.


> > But as soon as a photon is absorbed by an electron,
> > the photon's probability wave collapses,
>
> This is incorrect, as far as I understand it. OK, well, for the kind of
> "absorb" you're talking about, where the photon turns into a higher energy
> band of electron "orbit", that might be right. But not for simple "change of
> direction" kind of absorption.

What on earth should a "change of direction kind of absorption" be?

Strictly speaking, there is no such thing as a change of direction in a photon
anyway - there is just interference of its probability wave with itself,
because of disturbances in spacetime ("gravitation lenses") or the
electromagnetic field (due to the presence of charged particles). Which, at a
non-relativistic, non-quantum newtonian scale, can be described by the concept
of "light rays", but in quantum world there is no such thing.


> > so the re-emitted light's probability wave has no way of interferencing with it,
>
> Also incorrect. You can get interference between two photons that aren't
> even in the same light cone any more.

I'm not sure about this one - but if this is actually the case, then the effect
is obviously limited to the time when *both* photons "travel", i.e. exhibit
probability wave nature. As soon as one of the photons is absorbed, the other
can't interfere with it anymore.


> I think we're talking about different types of absorption and re-emission.
> I'm talking individual photons interacting with individual electrons. I.e.,
> I'm talking about the scale where it's nonsensical to argue whether it's the
> "same" photon or a "different" photon.

Individual photons can't interact with individual electrons unless they collapse
their probability wave and choose a particular electron to interact with.

At that moment, the interaction of the photon with the electron constitutes a
quite precise "measurement" of the photon's location (which turns out to be
identical to the electron's, with only the wavelength and the electron diameter
posing a bit of uncertainty), and therefore according to Heisenberg's
uncertainty relation the photon's impulse (and therefore direction) gets
somewhat wishy-washy.


> Light "bounces" off the electrons of an atom. Whether you want to call it
> "absorb and re-emit" or whether you want to call it "bounce" simply depends
> on whether you want to think of it as the same photon or a different photon,
> which is a question that makes no sense.

Fine. So we have "bounce" back in the dictionary, which was my initial intention
in this argument.

But the question *does* make sense from a quantum physics point of view: There's
a difference between a photon's *probability wave* "bouncing off" a whole bunch
of electrons all at once (by interferencing with itself due to the disturbance
in the EM field caused by the charged particles), or a photon actually
*interacting* with an individual electron in an "absorb and re-emit" kind of
fashion.

The former doesn't do anything to any individual electron. The latter does.

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Darren New wrote:

> 
> [Snip]
> 

So ... now we're starting to get an idea of how light behaves at a 
quantum level? [Sigh] ... The simple "light bounces randomly" is so much 
easier of an explanation ;)

-- 
~Mike

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Mike Raiford wrote:
> Darren New wrote:
> 
>>
>> [Snip]
>>
> 
> So ... now we're starting to get an idea of how light behaves at a 
> quantum level? [Sigh] ... The simple "light bounces randomly" is so much 
> easier of an explanation ;)

Aye to that. And DKB said, "let there be light," and it was good, 
although only an approximation to what he had in mind. :)

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clipka wrote:
> but the stimulating photon is *not* absorbed.

OK. But what I was saying is that your statement ""If you deal with 
fluorescence you'll see that *all* re-emitted light is *undirected*"" isn't 
true in general of all re-emitted light, since non-spontaneous emission can 
be caused to be directed.

>> Maxwell's equations are a statistical summarization of the actual behavior.
> 
> Nay. They are an *exact* description of the *waveforms* which *determine*
> statistical behavior (the "probability wave" of a particle between actual
> interactions).

I'm pretty sure we're agreeing here. "description of the probability wave 
which determines statistical behavior" is pretty much a "statistical 
summarization of actual behavior (of individual particles)", in my book.

>> Sort of. What would keep interference from working between an absorbed
>> photon and a re-emitted photon?
> 
> The fact that the photon has at last stopped being a wave (having just a certain
> *probability* to be somewhere) and started being a particle (actually
> interacting *somewhere* particular).

But if you don't actually "measure" that interaction, it doesn't turn into a 
particle. You can get interference between particles that have already been 
measured, so I'm not sure what your point is?

I suspect we're both, at this point, arguing nonsense, as it's impossible to 
tell whether a photon has "reflected" off an electron or been "absorbed and 
reemitted" as another photon. You're arguing you can tell the difference. 
Everything I've read says photons "interact" with electrons in exactly one 
way, characterized by electron charge, electron mass, and polarization of 
the respective particles.

> It is also described of the "probability wave" of the photon having "collapsed".
> 
> That's the moment where Maxwell can go home, and have a break until another
> photon is emitted.

How do you measure the difference between a photon being absorbed and an 
identical one being reemitted, or the same photon taking a different path, 
or a photon "reflecting" off an electron?

> What on earth should a "change of direction kind of absorption" be?

Like what happens when light goes through a lens. It interacts with the 
electrons in the glass and winds up moving at a slower speed therefrom. Why 
would a lens change the average speed of light if not because it's spending 
time being absorbed and reemitted?

> Strictly speaking, there is no such thing as a change of direction in a photon
> anyway 

In QED terms, there's no such thing as the direction of a photon at all. :-) 
That's why I said above we're both kind of arguing nonsense now.

>>> so the re-emitted light's probability wave has no way of interferencing with it,
>> Also incorrect. You can get interference between two photons that aren't
>> even in the same light cone any more.
> 
> I'm not sure about this one - but if this is actually the case, then the effect
> is obviously limited to the time when *both* photons "travel", i.e. exhibit
> probability wave nature. As soon as one of the photons is absorbed, the other
> can't interfere with it anymore.

This is counter to my understanding.
http://en.wikipedia.org/wiki/Delayed_choice_quantum_eraser
You can wait until after the photon has hit the detector, then determine 
whether you'll see interference or not.

> Individual photons can't interact with individual electrons unless they collapse
> their probability wave and choose a particular electron to interact with.

I don't believe that's correct. I'm certainly not well-schooled in this, but 
I don't believe an "unobserved" interaction with an electron by a photon 
will collapse the probability wave, or one would not have "virtual photons" 
and "virtual electrons" interacting with real photons and electrons.

You may be right, tho.

> But the question *does* make sense from a quantum physics point of view: There's
> a difference between a photon's *probability wave* "bouncing off" a whole bunch
> of electrons all at once (by interferencing with itself due to the disturbance
> in the EM field caused by the charged particles), or a photon actually
> *interacting* with an individual electron in an "absorb and re-emit" kind of
> fashion.

OK.

-- 
   Darren New, San Diego CA, USA (PST)
   The NFL should go international. I'd pay to
   see the Detroit Lions vs the Roman Catholics.

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