3.9
Growing under lights
3.9.1 Spectrum (colors) of light and it’s impact on plants
3.9.2 Horticultural Vs household lamps
3.9.1 Spectrum (colors) of light and it’s impact on plants
3.9.2 Horticultural Vs household lamps
Light intensity is measured / expressed in
various ways. One of the oldest measures of light is the foot-candle
(abbreviated fc).
A fc is an old English measure. It defines
the light projected by a standardized candle over an area of
one square foot from a distance of one foot. Back then,
before electricity, that’s how people read, by the light
of a candle.
Another way to measure light is by Klux
(stands for kilo lux or 1,000 lux). The lux (plural luxes,
abbreviated lx) is the International System unit of
illumination, equal to one lumen
per square
meter.
One fc is also
one lumen but per square foot. One Klux
equals approximately 92.3 fcs.
Other methods for measuring light will be
in mE/m2 = milli-einsteins per square meter per second, or in
Watts/m2 = watts per square meter,...
Most books about growing orchids refer to
light levels in fcs, so that’s the measure we’ll
use for this chapter.
Orchids in the wild are widespread, growing
in the dim light of a rain forest or in the bright light of a
mountain slope. Therefore we’ll encounter orchids that
need relatively low light conditions, other that need moderate
light and some that need bright light.
I often hear people say “I have my
orchids in a very bright location, it’s by a north facing
window” or “my orchids get plenty of light, there
are in the middle of the room under a skylight”.
Sorry folks but what your plants are
getting is what we, humans, consider bright light, but this is
far from being bright light for your plants.
On a bright early September day, at noon,
I measured the outside light and the light in a south
facing kitchen. The outside light was 8,000 fcs. The
south facing kitchen has a sliding door opening to the
south. It has a 2 1/2 feet by 5 feet window facing south
and it has a 3 feet by 5 feet skylight in it. The walls
are light cream and the floor is light green-white tile. There
are no trees or tall buildings to reduce the light entering
this room. This is a bright room by
any measure.
Here are the results in fcs:
I also measured the light at a north facing
window in the living room. The living room has an true
east window, a south facing sliding door and a large window on
the north side. Here are the light levels:
As these measurements show the light levels
drops very fast with as you move away from the sources of light and there is a vast difference in the amount of
light depending on the exposure of the window. Remember none of
these windows is shaded by trees or other buildings.
Let me try to illustrate how light diffuses
with an example. Let’s assume we build a pyramid whose
base is 8 feet by 8 feet and it’s height is 8 feet.
The construction is such that no light escapes from the
inside and no light penetrates from the outside.
At the inside top of this pyramid there is
a 1,000 watts light bulb emitting approximately 9,230 fcs of
light (now remember that’s the measure of light on a one square foot
area at a distance of one foot from
the light source).
At the base of the pyramid the area
illuminated by this bulb is 8 feet by 8 feet = 64 square feet.
As it is the same amount of
light (9,230 fc) that reaches
this 64 SF area, the illumination in fc at the base of the
pyramid is 144 fc (9,230 : 64).
Here is another way to illustrate this.
Let’s assume we have a square basin 1 foot wide and 1
foot tall. The volume of this bucket is one cubic foot of
water. Let’s imagine for the sake of our discussion that
the height of the water can be converted into imaginary
foot-candles and that 1 foot of water height equals 1 imaginary
foot-candle. So if we measure the height of the water in the
bucket we’ll find it to be one foot and therefore one
imaginary foot-candle.
Now let’s pour our bucket of water in
a square basin whose sides are two feet wide. The surface of
this basin is 4 square feet. Simple math’s will show that
the height of the water in this basis will only reach 1/4 a
foot which translates into one quarter of our imaginary
foot-candle.
And if we poured this same bucket of water
in a square basin whose sides are 3 feet wide, thus with a
square surface of 9 square feet, the height of the water will
only reach 1/9 of a foot which translates into 1/9 of our
imaginary foot-candle.
Light, like the water in our basin, will fill all the available space at any given
area. Since the total amount of light is
the same at any given area, the further away we are from the
light source, the larger the
illuminated area is and the less amount of light will fall on any given
square foot of area.
You can measure light with a light meter.
Good ones are available between $ 80.00 and $ 150.00.
Some measure light in foot-candles and others in luxes of
Klux’s
You can also use a 35 mm camera to measure
light. Here is how to do it:
• Set the camera at 25 ASA.
• Set the shutter speed at 1/60 of a
second.
• Place a white sheet of paper where
the leaves of the plants would be.
• Focus on the white sheet of paper
from a distance of 1 foot.
• Make a note of the f/stop shown in
the viewfinder.
Here are the approximate foot candles
corresponding to various f/stops:
f/2 = 100 fc
f/2.8 = 200 fc
f/4 = 375 fc
f/5.6 = 750 fc
f/8 = 1,500 fc
f/11 = 2,800 fc
f/16 = 5,000 fc.
Remember the maximum
light should be at noon on a
bright summer day.
Let’s start with the maximum light :
at noon, on a bright, cloudless summer day, the light level
outdoors (in the northeast) will top 10,000 fc.
We usually consider the light in a
supermarket to be bright. If we measured that light level
with a light meter we’ll find it’s intensity is
about 200 to 300 fc, and for us, humans, these 200 or 300 fc of
light intensity in the supermarket are quite comfortable.
But 200 to 300 fcs of light is just a
pittance for orchids.
Please keep in mind these levels of light
are for mature plants and the maximum light is for a limited time at
the brightest moment of the day (noon in a bright, cloudless, summer day).
Please also keep in mind you can acclimate
some of your orchids to grow a little outside of these ranges,
within reason of course.
The book “An Introduction to Orchids
- A Guide to the Growing and Breeding of Orchids”
published by The South Florida Orchid Society(Tel 305-226-4757)
and the book “All About Orchids” published by Ortho
Books both have very clear charts about light requirements of
orchids.
In practical terms what this means is that
to provide the minimum light our orchids need to grow and bloom we’ll
have to grow them :
Please keep in mind we are talking about windows that are not shaded by trees or other
buildings.
Your orchids will, to some degree, adapt to
their environment. You may be able to coerce a medium
light plant to grow and bloom on a bright east windowsill but
you’ll have a real hard time blooming a high light plant
on an east windowsill and very few, if any, will bloom on a
north windowsill.
Orchids will tolerate levels of light on
the higher end of their range provided the plant receives more
water (more frequent watering), more fertilizer and, if
possible, better air movement to keep their leaves a little
cooler.
When we say more frequent watering we mean
maybe every five days or so instead of every seven days, not every other day instead of every seven days.
This does not mean you should subject your
plants to excessive light. If your orchids get too much light and not
enough water and fertilizer, they will be stressed.
Stressed (weakened) plants have less
defenses against pests and diseases the same way as weakened
humans have.
Visible signs of stress are shriveling
pseudobulbs and / or leaves, drying buds, prematurely wilting
flowers,... Note that this kind of stress can also result
from unproper potting, decaying potting material, insufficient
watering,....
Watch the foliage of your plants. If the
leaves stay green, are crisp and firm, then the light is
probably right.
If the foliage is dark green, then the
light is too low.
If the foliage shows purplish marks or
coloration, then the light is probably too high.
Sometimes if the light is too high the tips
of the leaves will dry up.
Very few orchids will tolerate direct
sunlight, except maybe for an hour or too after sunrise and an
hour or two before sunset.
If you grow your orchids at a south or
southeast or southwest location, in a sunroom or in a
greenhouse, you’ll have to provide some shade, at least
for the brightest part of the day.
Surrounding trees or tall buildings may
provide enough shade, sometimes too much shade.
And remember, there is a substantial
reduction in the light from summer to fall to winter. Provide
more light / less shade as from mid October to mid February to
compensate for this natural reduction in light.
Finally remember that although plants will
adapt to changing environments, they will adapt better, with
less stress if you gradually ease
into the new conditions (such
as summering them in bright outdoors light).
My personal experience is limited as the
only plants I grow under lights are my flasks, but here is some
information to get you started.
If you look at a rainbow which diffracts
the components of light you’ll see the various colors of
the spectrum of light.
Natural light comprises ultra-violet,
violet, blue, green, yellow, orange, red and far-red light. And
there also is invisible infra-red light.
To us, humans, the green and yellow parts
of light are what is important for our vision, but these colors
are not that important to plants.
For plants, blue, red, far red and
infra-red light are the important parts of light.
The blue and red rays of light are
necessary for plants to photosynthesize.
Red light affects maturation, ripening and
dormancy of plants. Far red is necessary for plants to
grow. Far red and infra-red affect cell activity,
stimulate plant growth and development of new leaves and roots.
If we plan on growing under lights we have
to pay attention to the spectrum of light emitted by the lamps.
Horticultural lamps have been devised to
meet as best as possible the types of light necessary for plant
development which of course is not true for lamps developed for
human use as our light needs are not the same.
Horticultural lights are available as
fluorescent lights and bulbs.
Fluorescent lights are mostly rated in the
20 to 40 watts which translates into something like 185 to 370
fc of light.
Using several fixtures together will barely
produce enough light to grow low light orchids (Phalaenopsis,
mottled leafed Paphiopedilums,...) and then only if the
lamps are set only 8” to maximum 12” above the
foliage.
As their name indicate these lamps emit
substantially more light than fluorescent lights. There are
lamps of 100, 250, 400, 600 and even 1,000 watts, emitting
anywhere from 1,000 to over 9,000 fc.
These bulb lamps require special lighting fixtures that can cost anywhere from $ 150 to over $ 500.
Replacement bulbs cost anywhere from $ 35
or so for a 100 watt lamp to over $ 100 for a 600 watt lamp.
Most of them are rated for 10,000 hours of use which at
14 hours per day will last more than 2 years, so the cost of a
600 watt bulb is something like
$ 0.15 per day)
There are several brands available
(HydroFarm, Sun Systems, Philips Lightning,...).
These fixtures can be combined with a rail
system which moves the fixtures back and forth on a straight
line or that rotates the fixture allowing a greater growing
area.
Keep in mind the properties of light : at
2’ from the lamp you’ll get 1/4 the light emitted
by the lamp and at 3’ you’ll get 1/9 of the light
emitted by the lamp.
Many people have great success growing
under lights, in poorly lightly rooms, in basements, ...
The biggest challenge of growing under
light is managing the day & night temperatures, the
humidity and the air movement which is necessary to prevent hot
spots on the leaves.
Some of the information provided above was
derived from the book “Growing Orchids Under Light”
(by Charles Marden Fitch, published by the American Orchid
Society, Tel 561-404-2000, web: orchidweb.com) which I suggest
you buy if you are interested in growing under lights.
Also you may want to ask for the
Charley’s Greenhouse and Garden catalog ( Tel
800-322-4707, web : charleysgreenhouse.com) or for the
Worm’s Way catalog (800-274-9676, web : wormsway.com) as
both feature an extensive line of horticultural lights and
light fixtures.
A Comprehensive Guide to orchid Culture
Venamy Orchids
1460 Route 22
Brewster, New York10509
1460 Route 22
Brewster, New York10509
Toll Free
1-800-362-3612
1-800-362-3612
Fax
(845) 279-2682
(845) 279-2682
venamy@orchidsusa.com
Copyright 2002
Venamy Orchids
Venamy Orchids