I'm replying from work via Google and was going to reply to Janet but
for some reason she doesn't show up in google groups !?

( I'm not completely wrong, but definitely missing a big part of the
picture )

The sun does set later as you go west but because of the angle of the
earth's axis, it's not quite as simple as I suggested and is affected
by latitude too. That's sort of irrelevent though because as others
pointed out, it's the day length and strength of light that matters,
not what the time of day is.

So some other questions:

Is it better for plants to have long days of weak sun, or shorter days
of strong sun? At which latitude is the greatest total amount of
energy received from the sun each day?

How does it affect plants which are regulated by day length?

Is it the angle to the sun or is it the extra atmosphere that the
light goes through? If it's really just the angle, then I should be
able to get tropical levels of sunlight by rigging up a suitably
angled mirror to reflect the light. eg. at the poles, a mirror of
1m*1.41m at 45 degrees would catch 1 sq m of light and reflect it to
the ground as if it had come from directly above. Maybe this could be
designed into greenhouse roofs so that they had one side of the roof
angled with mirrors instead of glass to give the effect of direct
sunlight from above?

On 18 Mar 2004 07:07:44 -0800,
(Martin Sykes) wrote:

I'm replying from work via Google and was going to reply to Janet but
for some reason she doesn't show up in google groups !?

X- No Archive YES


( I'm not completely wrong, but definitely missing a big part of the
picture )

The sun does set later as you go west but because of the angle of the
earth's axis, it's not quite as simple as I suggested and is affected
by latitude too. That's sort of irrelevent though because as others
pointed out, it's the day length and strength of light that matters,
not what the time of day is.

So some other questions:

Is it better for plants to have long days of weak sun, or shorter days
of strong sun? At which latitude is the greatest total amount of
energy received from the sun each day?

In the tropics, where the sun is directly overhead.


How does it affect plants which are regulated by day length?

Is it the angle to the sun or is it the extra atmosphere that the
light goes through?

It's both.

If it's really just the angle, then I should be
able to get tropical levels of sunlight by rigging up a suitably
angled mirror to reflect the light. eg. at the poles, a mirror of
1m*1.41m at 45 degrees would catch 1 sq m of light and reflect it to
the ground as if it had come from directly above. Maybe this could be
designed into greenhouse roofs so that they had one side of the roof
angled with mirrors instead of glass to give the effect of direct
sunlight from above?

The trouble is that mirrors absorb some energy, because they are not
perfect reflectors. You can get the same effect, but with 100 %
efficiency by growing plants on terraces like they do with vines in
the Rhine and Mosel valleys.
--

Knowledge is knowing a tomato is a fruit;
Wisdom is not putting it in a fruit salad

On Thu, 18 Mar 2004 14:12:46 -0000, "Ophelia"
wrote:


In the height of summer it doesn't get dark and in winter I go to work in
the dark and return in the dark

Some work in the dark too. "My boss treats me like a mushroom, he
keeps me in the dark and throws crap on me... "

Best place for you ))

I said some, it's you who goes to work in the dark :-)

--

Knowledge is knowing a tomato is a fruit;
Wisdom is not putting it in a fruit salad

On Thu, 18 Mar 2004 14:12:46 -0000, "Ophelia"
wrote:


In the height of summer it doesn't get dark and in winter I go to work in
the dark and return in the dark

Some work in the dark too. "My boss treats me like a mushroom, he
keeps me in the dark and throws crap on me... "

Best place for you ))

I said some, it's you who goes to work in the dark :-)

--

Knowledge is knowing a tomato is a fruit;
Wisdom is not putting it in a fruit salad

The message
from (Martin Sykes) contains these words:

I'm replying from work via Google and was going to reply to Janet but
for some reason she doesn't show up in google groups !?

I'm ex-directory.

( I'm not completely wrong, but definitely missing a big part of the
picture )

The sun does set later as you go west but because of the angle of the
earth's axis, it's not quite as simple as I suggested and is affected
by latitude too. That's sort of irrelevent though because as others
pointed out, it's the day length and strength of light that matters,
not what the time of day is.

So some other questions:

Is it better for plants to have long days of weak sun, or shorter days
of strong sun?

Surely that depends on the plant species.

At which latitude is the greatest total amount of
energy received from the sun each day?

0? The tropics? Remember, not all plants can cope with maximum sun
exposure..think of all the shadelovers under the canopy of tropical
rainforests. Gardeners in very hot climates often have to erect shade
cover over their veg.

How does it affect plants which are regulated by day length?

Is it the angle to the sun or is it the extra atmosphere that the
light goes through?

Is what it? (Or do I mean, "what is it"?)


If it's really just the angle, then I should be
able to get tropical levels of sunlight by rigging up a suitably
angled mirror to reflect the light. eg. at the poles, a mirror of
1m*1.41m at 45 degrees would catch 1 sq m of light and reflect it to
the ground as if it had come from directly above. Maybe this could be
designed into greenhouse roofs so that they had one side of the roof
angled with mirrors instead of glass to give the effect of direct
sunlight from above?

You've lost me.

Janet.

If it's really just the angle, then I should be
able to get tropical levels of sunlight by rigging up a suitably
angled mirror to reflect the light. eg. at the poles, a mirror of
1m*1.41m at 45 degrees would catch 1 sq m of light and reflect it to
the ground as if it had come from directly above. Maybe this could be
designed into greenhouse roofs so that they had one side of the roof
angled with mirrors instead of glass to give the effect of direct
sunlight from above?

No, because a shallower angle means the light has a longer route through
the atmosphere, so less of it arrives at the earth's surface. It's not
the angle of incidence in itself that matters, it's the effect that that
angle has in determining how much light gets here.
--
Kay Easton

Edward's earthworm page:
http://www.scarboro.demon.co.uk/edward/index.htm

On Wed, 17 Mar 2004 17:08:26 GMT, Janet Baraclough.. said:

[]
] Depends what you're growing and at what latitude. Jo is in France;
] further south and warmer than the UK with less cloud cover, more sun,
] and more intense light.
]
Hi Janet,

Well, colder winters, warmer summers. Unless she's all the way out by the coast.

She should do well with sun, her region is referred to as "the garden of France."
A quick trip to some places like Villandry will confirm it!

So I don't think too much sun will be a problem for her. I'd favor the
frequently proposed "living windbreak."

In our very windy garden we've got gooseberries along the south (and windy)
side, they actually offer a good deal of protection without cutting too much
light. Of course, I'm probably all of 60 miles north of Jo, so perhaps it's
much darker here...

-E

] In some circumstances, afternoon shade and wind shelter could be preferable.
] Hot afternoon sun and wind together is fine for herbs, maquis and
] coastal plants with narrow/ hard/ silvery leaves etc but can be a deadly
] combination for plants with large soft green leaves like tomatoes,
] lettuce, beans or potatoes.
]
] Janet
]
]
]


--
Emery Davis
You can reply to
by removing the well known companies

If it's really just the angle, then I should be
able to get tropical levels of sunlight by rigging up a suitably
angled mirror to reflect the light. eg. at the poles, a mirror of
1m*1.41m at 45 degrees would catch 1 sq m of light and reflect it to
the ground as if it had come from directly above. Maybe this could be
designed into greenhouse roofs so that they had one side of the roof
angled with mirrors instead of glass to give the effect of direct
sunlight from above?

No, because a shallower angle means the light has a longer route through
the atmosphere, so less of it arrives at the earth's surface. It's not
the angle of incidence in itself that matters, it's the effect that that
angle has in determining how much light gets here.
--

OK, imagine an torch pointing straight down onto your work surface. (Or do
it with a real one!) Now imagine it tilted at an angle - it's obvious that
the same amount of light is spread out over a much greater area of the
surface. Likewise there is less light energy per unit of surface area when
the sun's lower in the sky.

As Kay points out, there's also the effect that when the sun is lower in the
sky, the light has to travel through more atmosphere is and gets dissipated
by this. So you can't use an angled mirror at sunset to get the effect of
noon at the equator!

If it's really just the angle, then I should be
able to get tropical levels of sunlight by rigging up a suitably
angled mirror to reflect the light. eg. at the poles, a mirror of
1m*1.41m at 45 degrees would catch 1 sq m of light and reflect it to
the ground as if it had come from directly above. Maybe this could be
designed into greenhouse roofs so that they had one side of the roof
angled with mirrors instead of glass to give the effect of direct
sunlight from above?

No, because a shallower angle means the light has a longer route through
the atmosphere, so less of it arrives at the earth's surface. It's not
the angle of incidence in itself that matters, it's the effect that that
angle has in determining how much light gets here.
--

OK, imagine an torch pointing straight down onto your work surface. (Or do
it with a real one!) Now imagine it tilted at an angle - it's obvious that
the same amount of light is spread out over a much greater area of the
surface. Likewise there is less light energy per unit of surface area when
the sun's lower in the sky.

As Kay points out, there's also the effect that when the sun is lower in the
sky, the light has to travel through more atmosphere is and gets dissipated
by this. So you can't use an angled mirror at sunset to get the effect of
noon at the equator!

If it's really just the angle, then I should be
able to get tropical levels of sunlight by rigging up a suitably
angled mirror to reflect the light. eg. at the poles, a mirror of
1m*1.41m at 45 degrees would catch 1 sq m of light and reflect it to
the ground as if it had come from directly above. Maybe this could be
designed into greenhouse roofs so that they had one side of the roof
angled with mirrors instead of glass to give the effect of direct
sunlight from above?

No, because a shallower angle means the light has a longer route through
the atmosphere, so less of it arrives at the earth's surface. It's not
the angle of incidence in itself that matters, it's the effect that that
angle has in determining how much light gets here.
--

OK, imagine an torch pointing straight down onto your work surface. (Or do
it with a real one!) Now imagine it tilted at an angle - it's obvious that
the same amount of light is spread out over a much greater area of the
surface. Likewise there is less light energy per unit of surface area when
the sun's lower in the sky.

As Kay points out, there's also the effect that when the sun is lower in the
sky, the light has to travel through more atmosphere is and gets dissipated
by this. So you can't use an angled mirror at sunset to get the effect of
noon at the equator!

"Glen Able" wrote in message
...
OK, imagine an torch pointing straight down onto your work surface. (Or
do
it with a real one!) Now imagine it tilted at an angle - it's obvious
that
the same amount of light is spread out over a much greater area of the
surface. Likewise there is less light energy per unit of surface area
when
the sun's lower in the sky.

As Kay points out, there's also the effect that when the sun is lower in
the
sky, the light has to travel through more atmosphere is and gets
dissipated
by this. So you can't use an angled mirror at sunset to get the effect of
noon at the equator!


I did mention both those points in my original question.

I still think the mirror has some benefit though - because the area of the
mirror is greater than the area of the greehouse floor, it's getting more
light into the greenhouse. I've drawn a diagram here :
http://www.users.globalnet.co.uk/~sy...reenhouses.jpg

In the standard greenhouse, some light just passes through without going
near the plants. In the modified one on the right, the roof is asymetrical
and internally mirrored on the side away from the sun so that that light
gets redirected to the plants. I bet it wouldn't be an expensive
modification and might make more of the little light we have. You could also
mirror the vertical side as well. Maybe even tin-foil would do the job?




--
Martin & Anna Sykes
( Remove x's when replying )
http://www.users.globalnet.co.uk/~sykesm

"Glen Able" wrote in message
...
OK, imagine an torch pointing straight down onto your work surface. (Or
do
it with a real one!) Now imagine it tilted at an angle - it's obvious
that
the same amount of light is spread out over a much greater area of the
surface. Likewise there is less light energy per unit of surface area
when
the sun's lower in the sky.

As Kay points out, there's also the effect that when the sun is lower in
the
sky, the light has to travel through more atmosphere is and gets
dissipated
by this. So you can't use an angled mirror at sunset to get the effect of
noon at the equator!


I did mention both those points in my original question.

I still think the mirror has some benefit though - because the area of the
mirror is greater than the area of the greehouse floor, it's getting more
light into the greenhouse. I've drawn a diagram here :
http://www.users.globalnet.co.uk/~sy...reenhouses.jpg

In the standard greenhouse, some light just passes through without going
near the plants. In the modified one on the right, the roof is asymetrical
and internally mirrored on the side away from the sun so that that light
gets redirected to the plants. I bet it wouldn't be an expensive
modification and might make more of the little light we have. You could also
mirror the vertical side as well. Maybe even tin-foil would do the job?




--
Martin & Anna Sykes
( Remove x's when replying )
http://www.users.globalnet.co.uk/~sykesm

The message
from "Martin Sykes" contains
these words:



"Glen Able" wrote in message
...


I still think the mirror has some benefit though - because the area of the
mirror is greater than the area of the greehouse floor, it's getting more
light into the greenhouse. I've drawn a diagram here :
http://www.users.globalnet.co.uk/~sy...reenhouses.jpg

In the standard greenhouse, some light just passes through without going
near the plants.

That doesn't make sense. To grow straight and evenly, plants need
light all around, and that's what they get in a standard GH. The uneven
light in a leanto GH makes seedlings lean to the lighter side, and
necessitates turning the trays or pots.

In the modified one on the right, the roof is asymetrical
and internally mirrored on the side away from the sun so that that light
gets redirected to the plants. I bet it wouldn't be an expensive
modification and might make more of the little light we have. You could also
mirror the vertical side as well. Maybe even tin-foil would do the job?

The sun moves across the sky so doesn't always fall on the mirrors;
when it doesn't, any potential benefit is lost. Meanwhile, the mirrors
constantly reduce light from their dark side.The plants are alternately
fried, and drawn.

:-)

Janet.

The message
from "Martin Sykes" contains
these words:



"Glen Able" wrote in message
...


I still think the mirror has some benefit though - because the area of the
mirror is greater than the area of the greehouse floor, it's getting more
light into the greenhouse. I've drawn a diagram here :
http://www.users.globalnet.co.uk/~sy...reenhouses.jpg

In the standard greenhouse, some light just passes through without going
near the plants.

That doesn't make sense. To grow straight and evenly, plants need
light all around, and that's what they get in a standard GH. The uneven
light in a leanto GH makes seedlings lean to the lighter side, and
necessitates turning the trays or pots.

In the modified one on the right, the roof is asymetrical
and internally mirrored on the side away from the sun so that that light
gets redirected to the plants. I bet it wouldn't be an expensive
modification and might make more of the little light we have. You could also
mirror the vertical side as well. Maybe even tin-foil would do the job?

The sun moves across the sky so doesn't always fall on the mirrors;
when it doesn't, any potential benefit is lost. Meanwhile, the mirrors
constantly reduce light from their dark side.The plants are alternately
fried, and drawn.

:-)

Janet.