Light in Orchid cultivation

Sunlight has several ' photomorphogenetic influences ' upon plants such as inducing photosynthesis , phototropism and photoperiodism . Light is essential for plants in many ways - it provides the energy necessary for the manufacture of carbohydrates , and it helps the mature plant to flower. bud initiation in plants is the result of the action of a hormone , the phytochrome , which requires for its production the correct duration of light and dark periods.

Light requirements of orchids vary from genus to genus .Cypripedium and Phalaenopsis need only between 200-300 foot candles of light (sunlight is equivalent to 10,000 foot candles ) and hence are to be kept in the comparatively more shaded regions of the orchid house . On the other extrem are genera like Vanda , Arachnanthe etc. Which thrive under 8000 foot candles of light. In such cases as much of sunlight as the plant can withstand without causing injury to the leaves , can be beneficial . In between these two extremes ,the optimum which orchids generally require is between 3000- 6000 foot candles.

An intimate knowledge of the light requirements of orchids has led to the development of the fascinating procedure called ' light gardening ', which is now quite popular among orchid growers. There are particular regions in the spectrum of sunlight which aids particular processes in the physiology of plants . Thus the blue and orange-red regions of the spectrum aid in photo synthesis ,while absorption in the far red regions of the spectrum aid in photo synthesis ,while absorption in the far red region stimulates flowering . Based on this knowledge , extra amount of illumination is now being supplied to orchids either to supplement sunlight or to replace it entirely ,with the result that more vigorous growth and greater output of flowers are achieved . Several kinds of illuminants are now being manufactured in Western countries for this purpose ,each having its own spectrul emission characteristic - some strong in blue , some in red etc. Pioneer among these was the ' Gro Lux ' lamps developed by the Sylvania Electric Products Inc. , Salem , Massachusetts in 1961 . For proper growth and flowering ,flourescent as well as incandescent lights are necessary . Flurescent lights produce the spectral curve of photosynthesis - high in red and blue rays and low in yellow and green , and are purplish in colour . The intensity of this illumination is usually very high. Incandescents on the other hand , are rich in far reds, stimulating photoperiodic responses . Only low levels of intensities needed here - 50 to 100 foot candles or even as low as 2 to 10 foot candles in some cases . Also , this illumination need be given only for short periods. The ratio between the two types of illuminations received by the plants is important in the production of flowers ,and this ration varies with each species . Walker and Abernathie (1964) suggest using 3 watts of flurescents to every 40 watts of fluorescents. Usually best growth and flowering have been obtained by using a combination of red (6000- 7000 Angostrom) and blue (4000- 5000 A) flurescent bulbs with 5 to 10 % visible radiation from incandescent bulbs. Usually when tubes are mounted , reflectors are also used to increase the intensity of light . Fluorescents could be kept as near the plant as possible but not so incandescents , since the latter heats up the atmosphere . Light gardening has made it possible to grow orchids even in cellars where no sunlight penetrates.

When electric lights are used in orchids houses , care should be taken to avoid their indiscriminate use . Green lights of low intensities are preferred for this purpose , since they interfere the least with the metabolic processes of the plant .

The majority of orchids are day-neutral ,ie . they are not influenced by day-length . Because of this, any amount of extra illumination given , could only be beneficial to these plants. By giving 24 hours of fluorecent illumination , seedlings , seedlings , particularly plantings developed from meristem culture , are made to grow and attain maturity much faster .