Alain wrote:
> Receive visible light, absorbs it and transform it to heat, re-emit it 
> as thermal infrared light. Energy in = energy out.

Haven't you heard of launching lasers and light sails? :-) Anyway, you 
*can* hold energy from absobed light indefinitely. That's what 
photosynthesis does.

-- 
Darren New, San Diego CA USA (PST)
   I am in geosynchronous orbit, supported by
   a quantum photon exchange drive....

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In article <408c3d0f$1@news.povray.org>, Darren New <dne### [at] sanrrcom> 
wrote:

> Haven't you heard of launching lasers and light sails? :-) Anyway, you 
> *can* hold energy from absobed light indefinitely. That's what 
> photosynthesis does.

But you can't continue to accumulate it indefinitely...for example, if 
the stored energy were never used, plants would eventually run out of 
CO2 and H20 to build the sugars which they store the energy in. You will 
eventually reach some equilibrium where total input == total output. 
However, if albedo includes radiation as well as reflection, then 
objects like suns and gas giants have albedos greater than 1.

Also, albedo could be used to refer specifically to visible light...in 
which case it would actually be possible for the reflective albedo to be 
greater than 100%, due to fluorescent materials on the surface. 
Extremely unlikely on a dead rock, though a planet with a large amount 
of fluorescent plant life could do it naturally.

-- 
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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Christopher James Huff wrote:
> But you can't continue to accumulate it indefinitely

Sure you can. You build oxygen and sugar from CO2 and H2O and photon 
energy, and then you dump the resulting high-energy chemical bonds into 
the environment. Someone else will eat it, and potentially emit more 
radiation than they absorbed.

Someone wrote "Truth: A body cannot reflect less light than is applied 
to it."  That particular statement is just not the truth without some 
qualifiers like "for a large enough body (but not too dense) over a long 
enough time." Radiation isn't conserved. Energy is conserved.

Granted, on something like a planet, the difference is likely to be small.

Follow-ups to off-topic.
-- 
Darren New, San Diego CA USA (PST)
   I am in geosynchronous orbit, supported by
   a quantum photon exchange drive....

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Alain wrote:
> Dan P nous apporta ses lumieres ainsi en ce 2004/04/25 13:04... :
> 
>> Jellby wrote:
>>
>>> Among other things, Dan P wrote:
>>>
>>>> Truth: A body cannot reflect less light than is applied to it.
>>>
>>> Huh?
>>
>> Yep; strange to think that way, I know, but that is a truth!
>> (Please don't bring up black holes either -- we aren't modelling those)
> 
> Receive visible light, absorbs it and transform it to heat, re-emit it 
> as thermal infrared light. Energy in = energy out.

Right; the light that is does not reflect it absorbs and converts to heat.
-- 
Respectfully,
Dan P
http://<broken link>

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Darren New wrote:

> Alain wrote:
> 
>> Receive visible light, absorbs it and transform it to heat, re-emit it 
>> as thermal infrared light. Energy in = energy out.
> 
> Haven't you heard of launching lasers and light sails? :-) Anyway, you 
> *can* hold energy from absobed light indefinitely. That's what 
> photosynthesis does.

Heat actually is a form of light. Actually, all matter is made of light 
as well.
-- 
Respectfully,
Dan P
http://<broken link>

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Christopher James Huff wrote:

> In article <408c3d0f$1@news.povray.org>, Darren New <dne### [at] sanrrcom> 
> wrote:
> 
>>Haven't you heard of launching lasers and light sails? :-) Anyway, you 
>>*can* hold energy from absobed light indefinitely. That's what 
>>photosynthesis does.
> 
> But you can't continue to accumulate it indefinitely...for example, if 
> the stored energy were never used, plants would eventually run out of 
> CO2 and H20 to build the sugars which they store the energy in. You will 
> eventually reach some equilibrium where total input == total output. 
> However, if albedo includes radiation as well as reflection, then 
> objects like suns and gas giants have albedos greater than 1.

Albedo does not include radiation by definiton. An object that emits 
light radiation, like a sun, is the light source!

Also, if you count radiation outside of the visible spectrum, an albedo 
will be a fraction of /all/ of that radiation, including the visible 
stuff, which would /still/ be a value between zero and one.

> Also, albedo could be used to refer specifically to visible light...in 
> which case it would actually be possible for the reflective albedo to be 
> greater than 100%, due to fluorescent materials on the surface. 
> Extremely unlikely on a dead rock, though a planet with a large amount 
> of fluorescent plant life could do it naturally.

Such materials emit light and, therefore, cannot be a valid part of an 
albedo value by definition. Albedos only concern /reflected/ light. If 
an albedo value is above 1, it is an error -- it is not a /valid/ value; 
it means that there is emissive material on the surface or a flaw in the 
instrument that is reading the value.
-- 
Respectfully,
Dan P
http://<broken link>

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Dan P wrote:
> Heat actually is a form of light.

No, it's a form of energy, specifically kinetic energy of atoms. Heat 
isn't measured in "photons". You seem to be confusing infrared photons 
with energy.

> Actually, all matter is made of light as well.

No. Matter is made of energy. (Actually, no, not really. But matter can 
be converted to energy and back again.) Light isn't energy, it's photons.

You seem to be confusing the concepts of "energy" and "light". A proton 
isn't made of photons (but rather quarks), but it can be converted to 
energy.

-- 
Darren New, San Diego CA USA (PST)
   I am in geosynchronous orbit, supported by
   a quantum photon exchange drive....

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In article <408c5c93$1@news.povray.org>,
 Dan P <dan### [at] yahoocom> wrote:

> Heat actually is a form of light.

Heat is a mass property of large groups of particles, related to the 
kinetic energy of the particles in the group. Heat is not infrared 
light, infrared just happens to be emitted by hot objects and readily 
absorbed by objects, heating them in the process. Hotter objects will 
emit in the visible range. Really, really hot objects emit in the 
X-ray/gamma range, but you don't really even have things like atoms at 
those energy levels.


> Actually, all matter is made of light as well.

Er, matter and energy are equivalent, and one can be converted to the 
other. Light is another form of energy, but saying matter is made of 
light is like saying mountains are made of stone walls because both are 
made of stone.

-- 
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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Darren New wrote:

> Dan P wrote:
> 
>> Heat actually is a form of light.
> 
> No, it's a form of energy, specifically kinetic energy of atoms. Heat 
> isn't measured in "photons". You seem to be confusing infrared photons 
> with energy.
 >
>> Actually, all matter is made of light as well.
> 
> No. Matter is made of energy. (Actually, no, not really. But matter can 
> be converted to energy and back again.) Light isn't energy, it's photons.
> 
> You seem to be confusing the concepts of "energy" and "light". A proton 
> isn't made of photons (but rather quarks), but it can be converted to 
> energy.

You're probably right; I'm confusing light with energy.
-- 
Respectfully,
Dan P
http://<broken link>

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Among other things, Christopher James Huff wrote:

> But you can't continue to accumulate it indefinitely...for example, if
> the stored energy were never used, plants would eventually run out of
> CO2 and H20 to build the sugars which they store the energy in. You will
> eventually reach some equilibrium where total input == total output.
> However, if albedo includes radiation as well as reflection, then
> objects like suns and gas giants have albedos greater than 1.
> 
> Also, albedo could be used to refer specifically to visible light...in
> which case it would actually be possible for the reflective albedo to be
> greater than 100%, due to fluorescent materials on the surface.
> Extremely unlikely on a dead rock, though a planet with a large amount
> of fluorescent plant life could do it naturally.

I albedo refers only to reflection, it cannot be higher than 1 and it can be 
certainly lower. The emr (electromagnetic radiation) absorbed and then 
emitted (possibly at a different wavelength) by the body is not reflection, 
it's (heat, black-body) radiation, fluorescence, or whatever.

If albedo refers to all kinds of emissions, it can be higher than 1. The 
Earth was probably born as a giant molten rock ball, now it has a more or 
less solid crust, some energy has been lost and radiated to outer space. 
The albedo can also be lower than 1 if the received energy is transformed 
to a different kind of energy and accumulated in the body itself.

If we are talking about a closed system (no exchange of matter) and in 
equilibrium (something not trivial), then yes, as much energy as it is 
received must be released. But energy is not only emr.

-- 
light_source{9+9*x,1}camera{orthographic look_at(1-y)/4angle 30location
9/4-z*4}light_source{-9*z,1}union{box{.9-z.1+x clipped_by{plane{2+y-4*x
0}}}box{z-y-.1.1+z}box{-.1.1+x}box{.1z-.1}pigment{rgb<.8.2,1>}}//Jellby

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