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Light Reflection through Glass Panes

Discussion in 'Everything Else Orchid' started by rico, Jan 25, 2017.

  1. rico

    rico Active Member

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    I'm doing a small talk on growing orchids in terrariums at the St. Paul Winter Carnival Orchid Show (if you're in Minnesota you should come to it (Jan. 28-29)at Marjorie McNeely Conservatory) and am seeking some help regarding light information. Unless I'm completely wrong, I recall hearing somewhere that for every "normal" pane of glass sunlight passes through, a certain percentage is reflected off and it decreases the intensity. I was hoping to use that as a justification/explanation to why you need supplemental lighting even when a terrarium is near a window. That way you get the best plant growth. This is what happened to me; my Nepenthes stopped pitchering once I brought it inside until I got some supplemental lighting. Anyway, I didn't feel comfortable using information that hadn't been substantiated by another source. If anyone else has heard of this "fact" and knows the actual percentage/amount of light that gets reflected I would be very appreciative. Thanks in advance!
     
  2. Ray

    Ray Orchid Iconoclast Supporting Member

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    There is no fixed percentage.

    The attenuation by the glass itself varies with glass formula and thickness. Fortunately, most tank glass is a general soda-lime formula, so that won't change enough to make much difference.

    At 2mm thickness, the perpendicular visible light transmission is about 95%. Double that, and its 95% of 95%, or about 90%. Note I said "perpendicular." If the light approaches the glass surface at an angle, more will be reflected. The greater that angle, the less goes through the glass.

    If the sunlight is coming through a window, then into the tank, in addition to those considerations, you need to consider that the windows might be a low-e glass that is coated with tin oxide, further reducing its transmission of visible wavelengths.
     
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  3. rico

    rico Active Member

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    Thank you Ray, that was very helpful.
     
  4. Marni

    Marni Well-Known Member Staff Member Supporting Member

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    I would add that if the light is coming from a window, all of the plants are going to be reaching for the light. Which would be away from the viewer. And good luck with your talk!
     
  5. rico

    rico Active Member

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    That's a good point Marni, I'll make sure to add it. Thanks!