Light Requirements Of Orchids
By Linda Fortner
Most plants, including orchids, require light to perform photosynthesis.

There are many kinds of orchids and each has a different lighting requirement due to where they live in their natural habitat. Some are exposed to a bright tropical sun while others live deep within shady forests. You need to learn what types of orchids you have and try to provide them with the same lighting levels they would normally receive in nature.

Light is measured in a unit called a footcandle (fc). A footcandle is equivalent amount of light that is produced by a candle at the distance of one foot. To give you an idea of light levels, on a clear sunny summer day at noon, the light in the sun would be over 10,000 fc. At the same time of day on a overcast winter day, the light level may be less than 500 fc.

You most likely will not be able to tell the true light level in an area because the human eye is too efficient at adjusting your vision to a broad range of light levels and can be fooled by the type of light present. For example, a grocery store may appear brightly illuminated with florescent lights, but in reality, the light level may be as little as 500 fc.

To determine the light level in the location you want to grow your orchids, you will need a light meter that will give you readings in footcandle units and is capable of measuring bright light up to at least 5,000 footcandles.

You can also determine the light levels at a location by using the built-in light meter of a SLR type camera.

In the descriptions of light requirements of orchids you may meet sweeping generalizations, which do not rally mean a lot, nevertheless, for the sake of completeness here is a table you might have seen innumerable times before:
Full Sun: Direct sunlight that's unobstructed for six to eight hours a day.
Partial Sun: About four hours of direct sun a day or lightly shaded sunlight all day.
Partial Shade: About two hours or less of sunlight a day.
Filtered Sun or Broken Shade: No direct sun, but some filtered light.
Dense Shade: No direct sun at all.

Please do not ask me how to tell apart

"lightly shaded sunlight all day"
from
"no direct sun but some filtered light"
or from
"no direct sunlight at all" ...

The orchid reaching for the sky can give some more useful advice !

 
 
TOO LITTLE LIGHT
 


How do I know if my orchids are not getting enough light? If your orchid is showing any of these signs, chances are it is not getting enough light:
  • Dark green leaves with no luster to them. The root system is fine.
  • Each new growth is smaller than the last growth.
  • Your orchid is floppy and very weak looking.
  • It has not bloomed or it has very few blooms.
How can I increase my light?
You need to move your orchids into a better light source, a different window, open the curtains, remove objects that maybe shading the window such as a tree or awning.

Be very careful when introducing you orchid (or any plant, for that matter) to more light because a plant that has been in poor light for any length of time will have very delicate leaves that can burn easily.

Move your plant to a higher light level gradually over several days. If you notice the plant leaves burning (they will turn brown and be very dry), move the plant further away from the light source or provide some shading for a week or two until the plant gets used to the increased light.

If you are growing your orchids under electric lights:
  • Reduce the distance between the light and the plant.

    NOTE: If you are using incandescent lamps, be careful not to place the plants too close to the hot light.

  • Move the plant toward the center of the light.

  • You should operate your lights 14 to 16 hours a day.

  • Make sure the bulbs are not over a year old, older bulbs tend to give out less light.

  • Use a special "grow light" in your fixture.
 
TOO MUCH LIGHT
 

How do I know if my orchids are getting to much light?

There are several ways you can tell if your orchid is getting too much light:

  • The leaves are showing burn spots. The spots can be yellow or brown dry patches on the leaves. They could also be rough and slightly raised.

  • The leaves feel hot to the touch. Leaves should be cool to the touch.

  • The leaves start turning black and dropping off.
    A plant exposed to too much sunlight will eventually die.

  • The plant's growth is stunted and the leaves start to turn yellow.

  • On some orchids, the color is bleached out of the leaves.

  • In other species the leaves become red. This is normal in case of several alpine orchids living in extemely bright but at the same time cold environments prevailing high up on mountains. However, for lowland species leaves turning into red may mean light levels already all too much for a particular orchid.

As far as utilization of light is concerned, it starts at light levels barely enough to the human eye to see anythig and gets saturated at light levels lower by several orders of magnitude than the peak sunlight is. Sunlight exceeding this saturation level is not a real problem - as long as the plant remains cool.

It is important to keep it always in mind that solar irradiation means not only light but heat as well - and this component is the one which is indeed important for most plants for causing overheating internally.

You may be surprised to hear that in you and your orchid are not really different in this respect.
Both in higher plants and in humans the same enzyme, namely isocitrate dehydrogenase becomes irreversibly denaturated just above 105 - 107 Fahrenheit degrees (41 - 42 ºC).

Neither humans nor orchids can tolerate so high internal temperatures for long periods, the consequences are sooner or later lethal.

How can I reduce the amount of light?

This is easier to control than not enough light.
  • Move the plant away from the hot sun. Remember that the heat component of the solar irradiation sun coming through a window is trapped in, heating the closed space. This is the (in)famous "greenhouse effect", which can be a mixed blessing, especially if that heating effect becomes all to much.
    The energy supplied by unquenched solar irradiation at sea level on the Equator may exceed two kilowatts per square metre per hour - more than enough to use your iron set to "linen" for the same period!
  • North of the Equator early afternoon sun is also much hotter than the morning sun, so move the plant to a East-facing window.
  • Place shear curtains in front of the windows.
  • Provide shade if growing outdoors. A plant that may be fine in the spring but could get burned as the sun moves higher in the sky toward summer.
    Increase ventilation
If you are growing under lights, you usually don't run into this problem unless you leave your lights on all the time or the lights are too close to the plants.
Burned leaves
This Cattleya left near to the closed window is a sorry example of the "greenhouse effect" explained above.
Quite probably in the open air the plant would have been just happy with the amount of light it received.
Dutch Gardens, Inc.
LinkShare Referral Prg
PETsMART
Select Blinds, Inc.
Teleflora Flowers
Good Times Entertainment
Western Union
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Measuring Light Levels With Single Lens Reflex Cameras
f-stop
DISMISS TABLE f/1.4 f/2 f/2.8 f/4 f/5.6 f/8 f/11 f/16 f/22
E
X
P
O
S
U
R
E

T
I
M
E
1/4
0.5
1
2
4
8
16
32
64
125
1/8
1
2
4
8
16
32
64
125
250
1/15
2
4
8
16
32
64
125
250
500
1/30
4
8
16
32
64
125
250
500
1000
1/60
8
16
32
64
125
250
500
1000
2000
1/125
16
32
64
125
250
500
1000
2000
4000
1/250
32
64
125
250
500
1000
2000
4000
8000
1/500
64
125
250
500
1000
2000
4000
8000
16000
1/1000
125
250
500
1000
2000
4000
8000
16000
32000
1/2000
250
500
1000
2000
4000
8000
16000
32000
64000
Light Intensity in footcandles (fc)
  • Set the film speed of your camera to 100 ASA/ISO.
  • Place a sheet of white paper in the location where you want to perform the measurement. Position the paper so it will receive highest light intensity possible.
  • Point your camera to the paper and get close enough to it so that the white paper fills the entire viewfinder. NOTE: You don't need to focus your camera.
  • Read the f-stop/exposure time values on your camera.
  • Find in the table above the corresponding light intensity in footcandles.
    Example: 1/125 sec exposure time at f-stop f/11 equals 1000 fc light intensity.