Orchid Care Tips: Light
Here is an exert from Orchids for Dummies...no pun taken please....a great book in my collection
Providing Light for Your Orchids
Adapted From: Orchids For Dummies
Different types of orchids have varying light requirements because they naturally grow in a wide range of habitats. Some thrive in full sun on exposed rocks, while others are at home in dense jungle shade.
The leaves of the plant give you some clue as to their light requirements (see Figure 1). Those with very tough, thick, stout, and sometimes narrow leaves frequently are adapted to very high light intensity. When the leaves are softer, more succulent, and wider, this is usually a clue that they're from a lower-light environment.
Figure 1: The type of leaf indicates an orchid's light requirements.
Your orchids will tell you by their growth habits and leaf color if they're getting adequate, too little, or too much light. When orchids are getting enough light, you'll notice the following:
The mature leaves are usually a medium to light green.
The new leaves are the same size or larger and the same shape as the mature ones.
The foliage is stiff and compact, not floppy.
The plants are flowering at approximately the same time they did the year before.
One of the more frequent results of inadequate light is soft, dark green foliage with no flowering. Another symptom of inadequate light is stretching, where the distance between the new leaves on the stem of orchids like paphiopedilum, phalaenopsis, or vandas is greater than with the older, mature leaves. On other types of orchids, the new leaves tend to be longer and thinner.
When orchids get too much light, their leaves turn a yellow-green color or take on a reddish cast and may appear stunted. In extreme cases, the leaves show circular or oval sunburn spots (see Figure 2). The sunburn is actually caused by overheating in the leaf. Although, in itself, this leaf damage may not cause extreme harm to the plant if the damage is isolated to a small area, it does make the plant unsightly.
Figure 2: A paphiopedilum leaf with a round or oval brown spot caused by too much light or sunburn.
If the sunburn occurs at the growing point, it can kill that leaf or the entire plant. Higher light intensities than are usually recommended are possible with some orchids if you increase the ventilation to lower these elevated leaf temperatures. Some orchid cut-flower growers like to push their orchids with the highest light intensity they can take without burning to yield the maximum amount of blooms. This technique isn't recommended for most hobby growers.
Measuring light intensity
Orchids that thrive in high light need several hours of direct sunlight (preferably in the morning to early afternoon), while those that thrive in lower light will perform with less direct and more diffused light in a windowsill or under artificial light.
Will you be growing the plants under artificial lights? Most light setups consist of multiple florescent lamps and can provide adequate illumination for medium- to lower-light orchids. High-intensity-discharge lamps are capable of much more light output but can be expensive to operate and generate quite a bit of heat.
How bright is your light? Figure 3 illustrates a simple yet effective and reasonably accurate method for determining the intensity of your light.
Figure 3: The shadow test is a simple and reasonably accurate way to measure light intensity.
No natural light? No problem!
Artificial light sources make it possible for everyone without greenhouses or bright windowsills to enjoy growing orchids in their homes. Although the limitations of what can be grown under these light sources are only restricted by equipment and electricity costs, it's a very practical method of growing for low- to medium-light orchids.
Fluorescent systems are still the most accessible and economical lighting systems to buy. Three-tiered light carts, are highly versatile and practical. Most of them are about 2 feet wide by 4 feet long, so their three shelves provide 24 square feet of growing area. If you grow compact orchids, this will be enough space to have at least one or more orchids in bloom year-round. If you collect miniatures, it will provide a growing space adequate for an entire collection. The convenience of such a cart can't be beat. You can place it in a heated garage, in a basement, or in a spare room.
When the orchids start to produce their tall orchid spikes, there usually isn't enough headroom under most fixed-height light units to accommodate this growing spike. At that point, you can move the orchids to a windowsill or use a light fixture that can be raised as the flower spikes develop.
Which bulbs or lamps you should burn in your fixtures is a highly debated topic. Years ago, the only real choice was cool white and warm white tubes. Some people still feel that a 50/50 mix of these tubes is the best option, because they're bright and very inexpensive.
Over 40 years ago, Sylvania started manufacturing Gro-Lux tubes — designed to provide light that more closely reflected the spectrum of light that plants use in photosynthesis, the process that plants use to produce their own food. This started a new race to produce the "best" plant bulb. The evolution of lamps has gone from the Gro-Lux to wide-spectrum bulbs and now to full-spectrum bulbs. The light cast by the full-spectrum lamp is supposed to most closely resemble natural sunlight. Viewed under these lamps, colors of the flowers are rendered more accurately.
Orchids can grow well under all these types of lamps. If you want to have the flowers appear most naturally colored under the lights and don't mind paying a premium for the lamps, the full-spectrum types are the best choice. The most economical pick — and still satisfactory — is the 50/50 ratio of warm-white to cool-white lamps. A compromise would be a blend of half warm-white and cool-white tubes and half wide- or full-spectrum lamps.
Newer to the artificial-light choices are high-intensity-discharge lights. These are very efficient in their production of light and are especially useful where you want to grow orchids requiring higher light intensities than fluorescent lamps can provide and/or where you want a greater working distance between the lights and plants
High-intensity-discharge lights do have the disadvantage of producing quite a bit of heat, so make sure not to get the plants too close to the bulbs.
The two most frequently used lamps for these systems are metal halide (MH) and high-pressure sodium (HPS). HPS is more energy-efficient than MH, but the light it emits is orange-yellow and distorts the color of the flowers and foliage. MH produces blue light that is more pleasing to the eye. Some manufacturers now produce lamps that combine the advantages of both.
Another newer option is the high-intensity compact fluorescent light. The fixtures for these look much like high-intensity-discharge (HID) units. They don't produce quite as much light as HID, but they have the advantage of producing little heat — so there is much less likelihood of orchids being burned.
If you're a beginner light gardener, then start with fluorescent-light setups, which are the most practical. Later, if you have the need, you can give the high-intensity-discharge lamps a try.