Re: [EnergyPlus_Support] Optical properties of glazing

["Michael J. Witte" <mjwitte@xxxxxxxx>]

To me it is all the same.  Transmittance and Transmissivity are both the ratio 
of what is transmitted to what is incident.  Likewise with 
reflectivity/reflectance.  I use the terms interchangably.  I see that both 
terms are used in the Engineering Reference, but I am not sure if the author 
intended to convey different meanings with -ance vs. -ivity.  The definitions 
below seem too detailed to me.  I would use the first definition as the basis 
for all of these:

Transmittance or transmissivity is the ratio of the total radiant or luminous 
flux transmitted by an object to the incident flux.  

Reflectance or reflectivity is the ratio of the total radiant or luminous flux 
reflected by an object to the incident flux.

Mike


On 28 Mar 2005, at 16:05, Fábyo Luiz Pereira wrote:

> 
>    Looking the Engineering Document, I have a question: for EnergyPlus, what is
> the difference between Reflectance and Reflectivity? Or Transmittance and
> Transmissivity?
> 
>    Studying the manual, I concluded that the difference is that reflectivity is
> the term used to account the angular dependence, while reflectance is used to
> express normal incidence.
> 
>    Searching on the net, i found the following definitions:
> 
> - Transmittance is the ratio of the total radiant or luminous flux transmitted
> by a transparent object to the incident flux, usually given for normal
> incidence.
> 
> - Transmissivity is the ratio of the directly transmitted light after passing
> through one unit of a participating medium (atmosphere, dust, fog) to the amount
> of light that would have passed the same distance through a vacuum. It is the
> amount of light that remains after the absorption coefficient and the scattering
> coefficient (together the extinction coefficient) are accounted for.
> 
> - Reflectance is the ratio of incident luminous flux upon a surface which is
> reradiated in the visual spectrum.
> 
>    Can I use this definitions for EnergyPlus?
> 
>    Thank you!
> 
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========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support      
EnergyPlus-Support@xxxxxxxx




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