Author: Amanda Sylvie

Garden & Greenhouse Magazine

The lighting you select for your plants can make the difference between active, consistent growth or stunted, mediocre growth. Lighting choices can result in rewarding blooms or years of waiting for a single bud. Orchids can be particularly picky about the light they receive, some requiring long days of high light while others are quite content with the low sunlight from a northeast-facing windowsill. Lighting is likely one of your greatest concerns as you begin bringing your plants indoors for the winter months. The other key time when lighting is especially important is when orchids are in an active growth phase.

Purpose of Light

Light is essential for plants to survive and grow. It is the most basic element of photosynthesis, the process of utilizing carbon dioxide and water to create oxygen and glucose, possible. Photosynthesis is how plants generate energy to grow, flower and fruit or seed. The amount of photosynthesis accomplished by a plant is impacted by the quality and interval of light the plant receives as well as the intensity of the light.

The intensity or brightness of the light, particularly natural sunlight, will impact the structure and color of the plant and its ability to flower. For example, a Dendrobium (an orchid that usually requires high-light) grown in low-light conditions will be spindly and light green, never blooming. However, if grown in conditions of higher light intensity, the Dendrobium will have thicker, stronger growths of a darker, more vibrant green color and will bloom one to two times a year.

The interval or duration of light the plant receives each day will impact the stress level of the plant. A low-light orchid growing in high-light conditions may show signs of leaf burn, pest infestation (due to lower resistance), and stunted or withered growth. Low light plants grow well in a north or east facing window or in a shaded area when grown outdoors. Moderate light orchids prefer filtered light through a south or west facing window or filtered sunlight. Some high light orchids need full sun with just enough cover to prevent leaf burn. There are many orchid species within each genera (or class) of orchids and all of the species within each genera may not have the same lighting requirements. However, below is a list showing the general light requirements of common orchid types.

Low light orchids- Paphiopedilum (Slipper Orchid), Phalaenopsis (Moth Orchid), Pleurothallis, Miltonia, Masdevallia, Bulbophyllum, Gongora, Stanhopea, Coryanthes, Odontoglossum

Moderate light orchids- Catasetum, Cycnoches, Miltonia, Oncidium, Cattleya

High light orchids- Vanda, Cattleya, Dendrobium, Grammatophyllum

The quality of the light plants receive may compensate, to some extent, for deficiencies in light intensity or duration. Light quality is especially important when using supplemental light or when you are growing plants solely with artificial lighting.

Types of Supplemental & Indoor Lighting

When choosing supplemental and indoor lighting for your orchids and plants, some things to consider are light quality, light cost, power cost, and light requirements of your plants. The types of lighting most commonly used are incandescent, fluorescent, HID (High Intensity Discharge), and the new kid on the block, LED (Light Emitting Diode).

Incandescent lights are the standard light bulbs typically used for room lighting. Most of the light put out by incandescent bulbs generates heat. This is one of the least efficient types of lighting for plants when considering energy use and benefit to the plant. The majority of incandescent light is emitted in the red and infra-red spectrum, which is great for flowering, but not ideal for optimal plant growth and health.

Fluorescent grow lights can be a lower cost solution for growing plants indoors over the winter months or for beginning seedlings. The bulbs begin to degrade upon use and have an expected useful life of 1 year. A fixture to house the bulbs is necessary. The majority of fluorescent bulbs produce blue light, which is beneficial for promoting photosynthesis, and the lights do not produce much heat. This allows growers to keep plants relatively close to the light, resulting in greater light intensity. Greenery grows extremely well under blue fluorescent lighting; just remember to move the lights up as the plants grow! Fluorescent grow lights that produce red light are also available to aid in budding and flowering. Bulbs may be mixed within the same fixture to help plants receive a broader spectrum of light.

HID lighting, either HPS (High Pressure Sodium) or MH (Metal Halide), are quite popular among growers who garden indoors year round. These lights are bright! HID lighting utilizes ballasts to manage voltage and current since they use 400-1000 watts. HID lighting also uses reflectors to improve light intensity. With the brightness of these lights, heat is an important consideration and fans may be necessary. Metal Halide lamps provide blue-spectrum lights and are good all-purpose lamps if you have a variety of plants. High Pressure Sodium lamps generate light in the orange/red spectrum to promote fruit and flower production. Since the output quality declines with age, lamps typically need to be replaced every twelve to fifteen months to ensure optimal plant growth.

Most folks are familiar with LED traffic lights, flashlights and commercial signs, but SolarOasis LED grow lighting for plants is new technology that many growers are just learning about. This lightweight grow light has targeted light output, promoting growth and blooming by delivering only the light colors specifically needed by plants. It saves on electricity costs as it only uses two to nine watts and runs cool to the touch to result in less radiated heat. A single professional model LED grow bar can be compared to 100-250 watts of traditional white light sources. The LED bulbs last from 20,000-100,000 hours which is 10 to 50 times longer than most conventional grow lights. SolarOasis LED light bars also require no ballast or reflector. At 21 inches long and 2-3 inches wide, they are quite small and can even fit under a cabinet for a kitchen herb garden. As they provide only the light colors needed for plants, they produce a pleasant, yet distinct, pinkish-purple light.

Measuring Light

If you know how much light your various plants or orchids require, it is a good idea to test the light levels using a light meter such as the Hanna Instruments Lux Meter. Light is typically measured in lux meters or foot-candle measurements. These are not equivalent measures, but can be converted from one to the other. The conversion is provided at the end of this article. Plants thrive when they receive twelve hours of their needed light level:

Low light requirements- 800-2100 lux (74-195 foot candles)

Moderate light requirements- 2100-5400 lux (195-501 foot candles)

High light requirements- 5400-10,800 lux (501-1003 foot candles)

Very high light requirements- more than 10,800 lux (more than 1003 foot candles)

Providing your plants with adequate light duration and intensity will ensure your plants are not only generating plenty of energy through photosynthesis, but that they are utilizing the fertilizer you are spending time, money and effort on applying.

How Much is Enough?

Besides using a light meter to determine how much light your plants are averaging, you may be able to determine your plants? needs by looking at their leaves. Plants receiving too little light tend to have larger or elongated leaves that are thin. They may also seem weak and have pale looking stems. Orchids that receive inadequate light usually display dark green, dull leaves, appear limp and have few or no blooms.

Once a plant has received its maximum intake of light in a day, excess light can be detrimental to the plant. You may notice burn spots on the leaves appearing as yellow or brown patches, shorter or smaller leaves, stem lesions and stunted growth.

If you notice any of these conditions and know that your plants do not have pests such as scale or mites, a change in light intensity, quality or duration will be necessary to ensure the plant will not only live, but grow and bloom.

For More Information?

In addition to local orchid and plant or gardening societies in your area, the extension services offered by any land-grant university in your state is a tremendous resource. In Texas, I often turn to http://texasextension.tamu.edu to find out what plants will thrive in our local climate. Extension services also provide invaluable information about general horticulture to include pest control, planting and harvesting dates, even hydroponics.

If the names of any of the orchids mentioned in the "Purpose of Light" section sounded unusual, but fascinating, you may enjoy looking them up on the Internet Orchid Species Photo Encyclopedia at http://www.orchidspecies.com/. Use caution, though, you may find yourself completely engrossed in this website hours later!

Conversion:
Foot candle = lux x 0.0929
Lux = foot candle x 10.764

The painting of Masdevalia Plum Wine is by Robin Street-Morris. Her works may be viewed at http://www.streetmorrisart.com.

Amanda Sylvie is the owner of Lone Star Orchids and may be contacted by calling 866.433.8256 or emailing info@lonestarorchids.com. You can visit her website at www.lonestarorchids.com.

This article was originally published in Garden & Greenhouse Magazine. Garden & Greenhouse is written for small commercial growers, hobby greenhouse owners and indoor/outdoor gardeners and is free to qualified readers. For more information visit http://www.GardenAndGreenhouse.net.

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