This month we welcomed a former member of the Society, Professor Andy Jones from the U.E.A.
whose talk was on growing orchids under lights. The talk was in three sections covering what the plants need in the way of light, how to provide the needs and how Andy achieves them.
All plants including orchids need light to photosynthesise and the amount of light that the plant receives has a direct influence on its growth. Unfortunately in this country the low levels of winter light has an inhibiting effect on growth and flowering. Also there are situations where one wishes to grow orchids, such as cellars or rooms with low levels of natural light where artificial illumination becomes essential.
Light encompasses a spectrum from infrared to ultra violet, with the visible spectrum having wavelengths between 400-700nM (nano metres). This divides into 3 colours, blue at 400-600nM, green at 600-700nM and red at 700nM, with blue and red being the key wavelengths. Blue light promotes vegetative growth and red promoting flowering and maturation of growth. There are 4 types of lighting used in providing an appropriate light source.
Fluorescent Tubes. Horticultural T5 tubes are best as they have a wide red to blue spectrum. They are cheap to buy and run but the output in lumens drops off with use. Usually placed 2-4 inches above the plants they run cool and produce a natural working light. On the minus side they are less powerful than other types and the tubes have a limited life.
High Intensity Discharge Lamps. These are ultra bright and can be used as the sole source of light in the growing situation. They require a ballast and double parabolic reflectors. They come in 2 types, metal halide which is near the blue end of the spectrum and high-pressure sodium which is closer to the orange-red end. Both produce higher lumens than fluorescent tubes and the higher the wattage the greater the area covered by the lamps. On the negative side they are more expensive to buy and run. They also generate considerable amounts of heat, which can scorch plants, and the light intensity can be a problem in the home.
Incandescent Lamps. These are mercury vapour lamps made for horticultural use, and look similar to energy saving bulbs. They have a good range of wavelength with the emphasis towards the blue end of the spectrum. These can be used in ordinary light fittings and are cheap to buy and run. They may be too hot for some light fittings and are not as flexible in use.
L.E.D. Lamps. This is the latest technology with the lamps being made up of diodes emitting both red and blue spectral lengths. They are cheap to run and have a long life, but the need to be placed close to the plants and are expensive to buy.
Andy concluded his presentation with images of his own growing set up. His collection houses a wide range of genera which all appeared to benefit from the increased light level. He also stressed the dangers of the combination of electricity and water, particularly in situations of high humidity and where spraying goes on. All circuits should be protected with circuit breakers and RCDs and ideally professionally installed.
It was a most interesting and dare I say it, illuminating, talk much enjoyed by the members present.