Black or green shade net?
blass
I read in the book, Orchids Of Asia by Teoh Eng Soon that green ranges
and green PVC as cover for orchids represses plant growth. Does this
cover green shade cloth rather than a black net? I'm using green shade
net. What's the difference between the two colors?
--
blass
?
Remember plant foliage tends towards green because they are pulling
the energy out of the red and blue ends of the spectrum.
I suspect, and will defer to the knowledge of those with greenhouses
and shadehouses, that use of green shade netting will lead to higher
measured light levels, but less light that is useful to the plants.
And on that thought, are there places that sell red/blue shade netting? :-).
>
>
--
Chris Dukes
Suspicion breeds confidence -- Brazil
Kenni Judd
blue.
--
Kenni Judd
Juno Beach Orchids
http://www.jborchids.com
Ray
In shade cloth, the solid material blocks the light, and the openings let it
pass, right? As an opening is an opening is an opening, what difference
does it make what color the light-blocking part is?
--
Ray Barkalow - First Rays Orchids - www.firstrays.com
Plants, Supplies, Artwork, Books and Lots of Free Info!
"Kenni Judd" <ke...@adelphia.net> wrote in message
news:JtCdnXJPNIC...@adelphia.com...
Ted Byers
"Ray" <ray...@firstrays.com> wrote in message
news:dKCdnaBxSu8...@comcast.com...
> OK, I give up.
>
> In shade cloth, the solid material blocks the light, and the openings let
> it pass, right? As an opening is an opening is an opening, what
> difference does it make what color the light-blocking part is?
>
(or that passes through translucent material) and the light absorbed. If
you shine white light on a green material, we seen green because most other
frequencies in the visible spectrum are absorbed and it is primarily green
light that is reflected. In the context of a greenhouse, then, you will
have light of various frequencies bouncing around, reflected by different
surfaces. An opaque green cloth will absorb the frequencies most useful to
plants and reflect those frequencies that are least useful to plants. This
is why, for example, leaves appear green; they absorb red and blue and
reflect green. I could go on, but I am sure those interested can find a
text on plant physiology or biochemistry.
It may help to think about the ultimate fate of the light that enters
through the openings in the shade cloth. While sunlight is nowhere near
white, lets assume that the light entering the greenhouse through the pores
in the shadecloth is white. What happens to it once inside. It bounces
around, reflected by one surface or another until it either escapes through
another pore or is absorbed. Since the plants will be absorbing red and
blue frquencies and reflecting green, the spectrum will increasingly include
primarily green colors. Similarly, if the shade cloth is green, any red or
blue light hitting it will be absorbed (and probably reradiated as
infrared), while the light reflected will be green.
Does any of this make a significant difference? I don't know since I have
not looked at, or conducted, any experiments that would tell us. I would
expect that there may be some effect on rates of primary production, and
thermal effects, but only a series of controlled experiments will tell us
for sure. I am not sure this is even important, except for those who design
and test shade cloth, since for ordinary growers and breeders, the
recommendations of how to use shade cloth will probably largely be based on
experience of how well different plants perform with different amounts of
shade cloth in different regions.
I don't know if this is helpful, but it is fun to think about.
Cheers,
Ted
--
R.E. (Ted) Byers, Ph.D., Ed.D.
R & D Decision Support Solutions
http://www.randddecisionsupportsolutions.com/
Healthy Living Through Informed Decision Making
Ray
diffraction around the edges of the openings, but I doubt it's significant.
My mind still wants to go back, though - if I have a white board and a green
board creating shadows, aren't the shadows the same?
Likewise, I suppose it's possible that some light is transmitted through the
mesh material, in which case the color might be important, but again I doubt
it's significant.
--
Ray Barkalow - First Rays Orchids - www.firstrays.com
Plants, Supplies, Artwork, Books and Lots of Free Info!
"Ted Byers" <r.ted...@rogers.com> wrote in message
news:qqudnfWRj_x...@rogers.com...
Ted Byers
>I had considered the fact that there might be edge effects - some slight
>diffraction around the edges of the openings, but I doubt it's significant.
>My mind still wants to go back, though - if I have a white board and a
>green board creating shadows, aren't the shadows the same?
>
However, don't forget that in the case of the shade cloth, you have the
pores that let some of the light through. What happens to that light? It
isn't all absorbed by the plants and fixtures in the greenhouse. Much of it
is reflected, and much of what is reflected will hit the inside surface of
the shade cloth. So the shade cloth is hit by light on both of its sides.
To see what I mean, you could try some ray tracing. Draw a cross section of
your greenhouse, with a solid floor and walls and roof that have gaps in the
line syou've used to represent them. Then, draw a series of parallel lines
hitting the greenhouse, representing incident light. Some of those will hit
the lines used to represent one of the walls or the roof. Those will either
end there or be reflected away from the greenhouse. Those that hit the
simulated pores will enter. Then continue those lines until they hit a
surface, and start drawing the path that would be taken by the reflected
light. Some of these will escape the greenhouse through the pores in the
shade cloth. Many, though, will hit the walls (shade cloth) and be
reflected back into the greenhouse. These paths will continue inside the
greenhouse until they happen to hit a pore, or until the light is absorbed
by something.
Energy is conserved. Light doesn't just enter the greenhouse and disappear.
Whatever isn't absorbed is reflected, and that reflected light must go
somewhere. The ray tracing exercise described allows one to see this, in
simplified form. A complicating factor is that any light absorbed is either
used by the plants in photosynthesis (converting electromagnetic energy into
chemical energy) or reradiated at a lower frequency (usually in the infrared
range), and this is reradiated in all directions. So, on average, half of
the light absorbed by the shade cloth will be radiated into the greenhouse
in the infrared, and half will be radiated out of the greenhouse.
Cheers,
Ted
blass
Thanks you guys and to Ted for that lengthy insightful piece. To quote
from the book, Orchids Of Asia by Teoh Eng Soon, top orchid grower of
Singapore, (Chapter 6 on Light)......
\"THE TYPE OF LIGHT IS ALSO IMPORTANT FOR THE PROPER GROWTH OF ORCHID.
LIGHT IN THE ULTRA-VIOLET, NEAR ULTRA-VIOLET AND GREEN RANGES REPRESSES
PLANT GROWTH, AND GREEN PVC SHEETS ARE TOTALLY UNSUITED FOR ROOFING OF
ORCHID HOUSES. WHEN TOO MUCH GREEN ALGAE COLLECT ON TOP OF THE PLASTIC
ROOFING, IT SIMILARLY REPRESSES PLANT GROWTH. THE ALGAE MUST BE
SCRUBBED OFF OR THE ROOFING REPLACED. THE SIMPLEST APPROACH IS TO
EMPLOY SHADING WHICH WILL NOT INTERFERE WITH THE NORMAL SPECTRUM OF
SUNLIGHT, SUCH AS WITH LATH HOUSES, WHITE PAINT OVER GLASS, OR BLACK
SARAN CLOTH.\"
Now comes the subject of the color black in shade net trapping heat
efficiently more than the green one. Any takers?
--
blass
Ted Byers
> Now comes the subject of the color black in shade net trapping heat
> efficiently more than the green one. Any takers?
>
Instead of answering directly, I'll put the question back to you in slightly
different terms.
NB.: A flat black surface is absorbing light energy in all frequencies in
the visible spectrum.
NB.: A green surface is absorbing all frequencies in the visible spectrum
EXCEPT for green. Green is reflected which is why it appears green.
Which do you suppose is absorbing more energy, assuming both are subject to
the same intensity of white light?
Which will reradiate more energy out of the greenhouse as infrared
radiation?
Which will reradiate more energy into the greenhouse as infrared radiation?
blass
I found a site (http://tinyurl.com/8znl8) selling shade nets. And this
is what they have to say or warn (darn, why now?) before buying their
shade nets:
*-Caution-
Green and black shade nets behave like filters. Essential radiation for
photosynthesis is reduced.
Thus, the growth is reduced. A green and black shade net decreases the
light’s quantity and spectrum quality.
White shade nets :
They decrease only light’s quantity, without altering luminous’
spectrum quality. As a consequence, the plant’s growth is faster with a
white shade net.*
--
blass
Ted Byers
"blass" <blass....@gardenbanter.co.uk> wrote in message
news:blass....@gardenbanter.co.uk...
What is said about green shade nets is obviously true. What is said about
black shade nets seems only partially true. While it is true that a black
material will reduce the quantity of light, I don't see how it can reduce
the quality of light (with respect to photosynthetically active radiation or
PAR) and appear black.
I can see how a black net can result in less PAR than a white one, due to
more of the light that is reflected inside the greenhouse being absorbed by
the interior surface of the net. But I'd hazard a guess that the effect of
a choice between white and black shade nets on photosynthesis would involve
a tradeoff between a little more PAR vs a little more heat.
Ray
that significant?
--
Ray Barkalow - First Rays Orchids - www.firstrays.com
Plants, Supplies, Artwork, Books and Lots of Free Info!
"Ted Byers" <r.ted...@rogers.com> wrote in message
news:U8KdnVljmNT_itje...@rogers.com...
Ted Byers
> Ah HAH! I had forgotten about the reflected light. Do you think it's
> that significant?
>
> --
It all depends on the details of the geometry of the structure. If the
geometry of the greehouse, and the properties of the shade cloth, are such
that a large proportion of the light entering the greenhouse is ultimately
absorbed inside the greenhouse (meaning used by plants to produce new
tissue, or ultimately converted into heat), then this effect may well
overwhelm the contribution to plant production from light that has entered
the greenhouse and not yet been reflected. On the other hand, if the
combination of the geometry of the greenhouse and the properties of the
shade cloth are such that most of the reflected light exits the greenhouse,
then the effect is likely negligible.
The only way to know for sure if the effect is likely to be significant is
to construct a computer simulation; a numerical experiment if you will. The
physics, and the computational requirements for ray tracing, is simple
enough. The data management, though, would be challenging, since you'd have
to run a reasonably large number of rays, simulating a constant input of new
rays, and keep track of rays that have left the structure or been absorbed,
until the system approaches equilibrium (probably reached almost instantly
in the real world, but likely to take some time in the simulation). You can
then estimate the proportion of rays striking a given surface that have been
bouncing around the greenhouse before striking the surface in question (and
do this for a number of different frequencies, simultaneously, to get a
sense of the impact of this effect on the spectral quality of the light. Of
course, once such a simulation model has been constructed, it is easily
modified to examine the consequences of using black shade cloth rather than
white shade cloth (or any other color for that matter), both for the quality
of light reaching a given surface and for thermodynamic effects.
While I am a specialist in environmental modeling, I am not sure I want to
spend the months needed to produce an application to do this to the
standards I maintain for my own work; especially when I am working hard on
getting a new business established. If I was working at some university,
though, I'd certainly assign it to graduate students to give them a sense of
the application of science in the real world.
Ray
the wavelength they don't use. Then we have to speculate on the
reflectivity of the benches, floor, media, algae, moss, etc.
My guess is that it's insignificant compared to the incoming light.
--
Ray Barkalow - First Rays Orchids - www.firstrays.com
Plants, Supplies, Artwork, Books and Lots of Free Info!
"Ted Byers" <r.ted...@rogers.com> wrote in message
news:XZKdnVWJIsMkfdje...@rogers.com...
Reka
says...
that I have grown up with. (Shades of those poor newbies who think this
is "rec.gardens.orchards"!) Over here, we have problems with hail damage
on apple crops from summer to early fall. Thus, hail netting is
stretched over the trees during that time period. Very dark green,
black, or white nets have been used. It has been proven that the red
apples under white netting color up much better than those under the
other two dark colors. Now, how this can be correlated to orchids, I
don't know, but perhaps it is worth the time I took to write it. And I
am a slow typer. :-) I am assuming it could be the extra heat generated
under the darker colors that prevent better color. Red apples need
temperature swings from cool nights to warmer days without rain in order
to color up well.
--
--
Reka
This is LIFE! It's not a rehearsal. Don't miss it!
http://www.rolbox.it/hukari/index.html
Steve
>................
> ...............................
> Okay, I know a little about orchids, but more about orchards, a subject
> that I have grown up with. (Shades of those poor newbies who think this
> is "rec.gardens.orchards"!) Over here, we have problems with hail damage
> on apple crops from summer to early fall. Thus, hail netting is
> stretched over the trees during that time period. Very dark green,
> black, or white nets have been used. It has been proven that the red
> apples under white netting color up much better than those under the
> other two dark colors. Now, how this can be correlated to orchids, I
> don't know, but perhaps it is worth the time I took to write it. And I
> am a slow typer. :-) I am assuming it could be the extra heat generated
> under the darker colors that prevent better color. Red apples need
> temperature swings from cool nights to warmer days without rain in order
> to color up well.
Hi Reka.
We haven't had one of those orchard/orchid confused people in a while now.
About the red apples under white netting... You are obviously right
about better color with cooler temperatures. That's why they grow a lot
of Macintosh apples in Vermont and here in northern New York but not
much farther south. I bet heat isn't the factor with the netting though.
I'm not sure a dark netting would cause more heat around the trees.
(Also not 100% sure it wouldn't.) I bet it's just more light getting
through. You KNOW the apples color up better on the sunny side of the tree.
My first thought was that maybe this does translate into better orchids
and the better light that colors up apples would probably help orchid
blooming. On second thought, if it's just the quantity of light, then
for orchids that need the shade, they need the right amount of shade and
it probably doesn't matter if that amount is created by black or white
cloth.
Steve
Ted Byers
> Well Ted, I guess we can ignore light reflected from the plants, since
> it's the wavelength they don't use. Then we have to speculate on the
> reflectivity of the benches, floor, media, algae, moss, etc.
>
from a plant appears green because there is more green light than anything
else, but that does not imply that there is no blue or red. Blue and red
light may well be present in the reflected light, but in equal values of the
plant looks green, or a bit more red if there is a reddish hue to the
leaves. From a scientific perspective, we can not say that all green light
is reflected by leaves, nor that all red and blue light is absorbed. All we
can say is that more green light is reflected by the leaves and more blue
and red light is absorbed. And of the light that enters the leaves, more of
the green light will pass right through while less blue or red light will
pass through. Most leaves are translucent; not opaque!
While I didn't mention it before, there is the question of light that passes
through the leaves. In most species, if you hold a leaf up to the light,
you can see light coming through the leaf, and this light is normally green,
and this happens even though you can not normally see anything on the other
side of the leaf. This will be greater or less depending on the species,
but the important point to remember is that there is no such thing as an
energy conversion process that is 100% efficiency. It is unusual to get
better than 5 to 10 % efficiency, although I suppose that with some
creativity, some engineer might come up with something better. In the
biological world, the vast majority of energy of light of any frequency is
either reflected or absorbed and converted to heat.
And you're right. If we are to be thorough, we'd have to consider
everything in the greenhouse. Consideration of allgae and live moss,
though, could be lumped together with the other plants in the greenhouse as
they'd have similar properties. As they'd all be using the same process of
photosynthesis, they'd all have very similar optical properties. Alas,
things get much more complicated as we consider them in more detail.
Here is a question that might help understand the implications of this. You
have two surfaces, both subject to the same white light. One surface
appears to be dark green and the other appears to be light green. Since
both are subject to the same white light, they both get the same amount of
green light. How, then does one appear lighter than the other?
Here is a tip, to help answer the above question: In computer graphics, one
can lighten the color green obtained from the brightest green setting for a
set of pixels by adding equal amounts of blue and red. You can break the
light coming from a pixel, in this context, into two components: one made of
pure green light and another made of white light. I use this routinely in
any computer graphics I add to my applications.
> My guess is that it's insignificant compared to the incoming light.
>
> --
I am not so sure. I will not say anything definitive, since I have not seen
reports of experiments designed to test it, nor have I done any myself.
However, theory suggests it could be significant and Reka has provided some
evidence that plants are affected by the color of netting used, in her case
for protection from hail, but the purpose of the netting is immaterial here.
Reka
says...
netting because of the glare. I wonder if the quality of the light is
different, though.
From an abstract:
"The effect of hail netting on light penetration and fruit quality was
evaluated in commercial apple orchards in Eastern Switzerland. Black
nets reduced light levels (PAR) by 18 to 25 %, white netting by 8 to 12
% and grey nets (black and white fibres) by 15 to 17 %. No definite
influence of black hail nets on maturity and fruit quality has been
observed under good conditions (weather, site, small trees with loose
canopies, optimal fruit load, etc.) and with varieties for which fruit
colour is mainly genetically determined. For ?Jonagold? the light
intensity is decisive for development of fruit colour. Reduced colour
development under black nets may be observed on this variety. The
harvest time can be delayed by 8 to 10 days. Flesh firmness, soluble
solids content and acidity were not affected. In general the external
and internal fruit quality depends on many other factors which are more
important than the effect of hail netting."
http://www.actahort.org/members/showpdf?booknrarnr=557_56
So it's a light/shade factor rather than a heat factar, though most
farmers here will swear that it is hotter under the darker nets.
Nancy G.
Ray wrote:
> Well Ted, I guess we can ignore light reflected from the plants, since it's
> the wavelength they don't use. Then we have to speculate on the
> reflectivity of the benches, floor, media, algae, moss, etc.
>
> My guess is that it's insignificant compared to the incoming light.
>
Not contributing much to the discussion, but I did research some
interesting articles regarding light used, benefits of reflection for
increased light, even an old comparison of light bulbs.
http://plasticulture.cas.psu.edu/DSuccess-mulch.htm
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1062077
http://www.ccpo.odu.edu/SEES/veget/class/Chap_3/3_1.htm
http://www.thekrib.com/Lights/intensity.html
My sun room uses transluscent insulation under a clear roof, unshaded
windows. I've considered adding mirrors or foil against the back wall
to try to limit the shadowed places and balance the development of
plants. The plants are outside during the summer and get good light
coverage from most directions, but the blooms concentrate on the the
sunny side of the plant during the winter. In the southeast area of
the room the blooms on the cattleyas develop in all directions around
the plant.
Someone that uses supplemental light may try using bulbs with enhanced
spectrum designs or colored reflectors and filters to increase
different light bands in the spectrum.
Orchids take such a long time, even a single bloom season. There may
be more in the color of the floor and encouraged reflection of the
walls than most people have given credit in their pursuit of light.
Don
benches, shade cloth and walls help our orchids? I have painted
surfaces white for total light intensity but could there be a colour
that would be an improvement?
Don
S.W. Ontario
Ray
(assuming all other mulch properties are identical)? Is it the reflected
red light back to the plant that makes a difference or is it a change in the
ground temperature under it?
--
Ray Barkalow - First Rays Orchids - www.firstrays.com
Plants, Supplies, Artwork, Books and Lots of Free Info!
"Don" <ha...@ican.net> wrote in message
news:e526f$43473270$d15a87ca$25...@PRIMUS.CA...
Ted Byers
> Doesn't that raise the question about what the red pigmentation does
> (assuming all other mulch properties are identical)? Is it the reflected
> red light back to the plant that makes a difference or is it a change in
> the ground temperature under it?
>
Both are likely to be happening. Any red light reflected onto a leaf will
likely contribute to photosynthesis, and possibly other processes. It is
certain that any light absorbed by the ground will be converted into heat,
producing nonlinear changes in soil temperature with depth. Now
understanding that process is considerably more complicated, involving
conduction and transport of heat, but the salient point is that light
hitting the soil will raise the temperature of the top layers of the soil,
and that will have the usual effect on reaction rates in the plant's roots.
How significant each process is is a different matter that can really only
be determined experimentally. I know the agriculturalists I know talkof the
importance of soil temperature, but I personally have not heard them discuss
the colour of the ground.
Cheers,
Ted
Don
The following is copied and pasted here from the Lee Valley site -
www.leevalley.com . Do orchids have this phytochrome, the colour
sensitive protein the stimulates rapid growth?
Don
Super Red Mulch
Super Red Mulch - Gardening
From time to time research comes up with some astounding results. This
is one of them.
When this red plastic mulch is put on the soil under tomatoes, it will
increase yields by up to 20% over black mulch, and makes the fruit set
earlier. It works by reflecting a certain spectrum of light back to the
plants, which in turn triggers the release of phytochrome, a
color-sensitive protein that stimulates rapid growth and development.
The research was done by a number of universities and our own tests
proved it accurate.
Kenni Judd
some "quality" reduction on a 1-1 basis, but it would take at least 2 [and
I'm afraid maybe more] similarly-rated layers of white to provide the shade
of 73% black [what we started with, for phals, and had to add more shade to,
here in So. Fla.]
Second-hand: Aluminet has a number of customers buying its red and gray
products, or so they told me when they were here trying to sell me ... Not
so much orchid growers, mostly growers of flowering terrestrials. According
to Aluminet, these big growers move blocks of plants under different colors
of shade to time their flowering. FWIW. Kenni
"blass" <blass....@gardenbanter.co.uk> wrote in message
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>
