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Thomas Olson
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A thermal masses job is to absorb light. What if I want red and blue light on the plants? Computer programs use red green blue, it seems to me FF00FF is the way to go, which is Fuschia. If I paint or dye the thermal mass Fuschia, will it do what I want it to do? When I think about it, that's the color that I see on LED grow lights.
 
Rory Rivers
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The thermal mass absorbs light and converts it to heat. So I would think you would want 000000 to absorb all the light. I wonder if there is a linear relationship like FF00FF reflects 2/3 of the light and 00FF00 reflects 1/3
 
Thomas Olson
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I'ld imagine most of the heat comes from the non-visible spectrum (infrared). I suspect the visual spectrum does provide heat as well, just not as much. Then again, I don't know what I'm talking about, that is why I'm asking. There are all kinds of thoughts going thru my head at the moment and I don't understand the science completely.
 
R Scott
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Location: Kansas Zone 6a
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There is probably a lot of plant specifics on this.

Like the red mulch plastic for tomatoes doesn't help other plants much: http://www.tomatodirt.com/red-plastic-mulch.html

I have also wondered about covering the mass with a reflective blanket in the summer to reduce heat gain, but that usually just cooks the plants with too much light and intense heat in the day. Better to control the light through shade cloth and keep the mass absorbing the heat instead of radiating it back to the plants when they don't need it.
 
Zach Weiss
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I don't know if the thermal mass is absorbing light so much as absorbing heat from the sun. The darker the mass the more heat it will retain.

One thing I've heard about thermal masses is that concrete is actually a better thermal mass for passive solar design. Water stores the most heat but has a lower thermal diffusivity and so it holds onto that heat for longer periods of time. Concrete and rock have a higher thermal diffusivity so they give off their heat more readily. The best is to use both so the water is releasing heat over longer periods of time while the rock is releasing heat each night.
 
Cory Arsenault
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Location: Ottawa, Canada
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The thermal mass doesn't really absorb the light directly.

The darker colours thst the thermal mass is usuallly painted, absorb the light. Black absorbs 100% of the light which is why black isn't really a colour, it's a lack of colour being reflected which is why black is the most effective for passive solar.

So the colour absorbs the "visible spectrum" light and converts it to infrared which is abridged by the thermal mass. A passive system usually has this themal mass behind a glass box, sometimes termed the aperture, which traps in the infrared energy.

The wavelength of visible light easily passes through glass but when it's converted to infrared by the colour black, the wavelength is downgraded and it can't pass back out through the glass again and gets absorbed through the thermal mass.

Or at least this how it's supposed to work.
 
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