[Stoves] radiant heat capture, total heat measurement

[ajheggie at gmail.com]

On Fri, 9 Mar 2012 08:58:19 -0400, Kevin wrote:

>It appears to me that the inability of window glass to pass UV and IR is a 
>"reflection phenomenon" rather than an "absorption phenomenon.".

I don't think so, I'm not a physics teacher and even 45 years ago I
wasn't a shining student but...
>
>Note that different coloured glasses absorb different light frequency 
>ranges. For example "Red Glass" absorbs all the light in the visible 
>spectrum EXCEPT for the frequencies in what our eyes tell us is "red light." 
>Red glass is thus opaque to blue and green light.

...thus clear glass is opaque to low energy, longer wavelength IR. One
of the phenomena of electromagnetic absorption is that the atoms in
the absorber can only accept the energy in discrete amounts, these
"bundles" of energy must match the absorbers excitation energies,
otherwise they pass through or reflect.
>
>Now, here is where the fun hits the fan: If red glass is transparent to red 
>light, what happens to the blue and green fractions of the incident 
>spectrum? Clearly, if the glass was reflective of the blue and green 
>fractions, then when we viewed the glass surface from the "Incoming light 
>side", the glass would appear to be blue-green, but when viewed from the 
>Outgoing light side", it would appear red. "Red Glass" is thus transparent 
>to Red light, absorptive of blue and green light, and reflective of UV and 
>Infra red light.

No I think it absorbs most of the UV (some is reflected) and the
longer wavelength IR, it passes the shorter wavelength IR. I agree it
absorbs the blue-green.
>
>Why are healthy leaves green? Very simple!!.... the Leaves are very good 
>absorbers of Red and Blue spectral fractions, and very good reflectors of 
>the Green spectral fraction. :-)

I think his is correct, the energy necessary for photosynthesis is
supplied by the higher frequency visible light.
>
>One thing that puzzles me is that when I went to school, in the "Olden 
>Days", there were three "Primary Colors"... Red, Yellow, and Blue.Now the 
>three primary colors are Red, Green, and Blue. I this progress, or what?? I 
>don't think so!! How do I make Yellow if I only have Red, Green and Blue 
>crayons? ;-)

The primary colours of our school days were to do with reflected light
so red, green and blue. Nowadays we think in terms of direct light
emitted from surfaces, like CRTs and LEDs. The emitters build colours
by adding red, blue and green, the reflectors build their colours by
what they don't absorb. If you mix all the emitters you get white
light, if you mix all the reflectors you get black.
>
>Best wishes,
>
>Kevin
>
>
>
>
>----- Original Message ----- 
>From: <ajheggie at gmail.com>
>To: "Discussion of biomass cooking stoves" <stoves at lists.bioenergylists.org>
>Sent: Friday, March 09, 2012 4:28 AM
>Subject: Re: [Stoves] radiant heat capture, total heat measurement
>
>
>> On Fri, 9 Mar 2012 03:35:06 +0000, Crispin Pemberton-Pigott wrote:
>>
>>>Because glass is a pretty good absorber of IR it is also a pretty good 
>>>emitter.
>>
>> Surely glass absorbs the higher energy spectrum we can't see in the UV
>> band ( which is why you won't get a tan beside a close window) and
>> passes visible light and higher frequency infra red from hot bodies,
>> like the sun, but absorbs the lower energy infra red from cooler
>> bodies like earth and our bodies. This is the "greenhouse" effect,
>> other substances act similarly but we'd best not go there.
>>
>> AJH
>>
>>
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>
>
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