[Radiance-general] Re: query about accurately modelling glazing

[Zack Rogers]

Hey Greg,

You may be right, I've wrestled with this quite a few times.  That was 
exactly my line of thinking until we got a composite translucent ceiling 
material measured with an integrating sphere and it resulted in a 
significantly different transmittance from the front the the back.  I 
think for a single surface this is exactly true (ie. a low-e film or a 
single pane of glass) but for a composition I think it can vary 
slightly.  Like a one-way mirror?  And using the example of a pane of 
glass with a low-e coating.  It seems like light striking that low-e 
surface from air's index of refraction could behave differently than 
light striking the surface from the glass's index of refraction. 
 Atleast thats how I justify it to myself...."do I lie to myself to be 
happy?"  But it also doesn't have to break the conservation of light 
laws, I don't think.  As an example, say of the light striking the low-e 
side of the composition, 70% transmits, 20% reflects, and 10% absorbs. 
 Then of the light striking the glass side of the composition say 75% 
transmits, 15% reflects, and 10% absorbs.  In both situations 100% of 
light is accounted for.  I am completely unsure on this issue.  Can 
anyone help explain?

Thanks for correcting and/or questioning my response Greg.
Zack

-- 
Zack Rogers
Staff Engineer
Architectural Energy Corporation
2540 Frontier Avenue, Suite 201
Boulder, CO 80301 USA

tel (303)444-4149 ext.235
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