Often when there is insufficiency of sunlight, you can compensate it by providing your plants with artificial light. The quality of artificial light, however, varies. In fact, the different type of light emitted by various bulbs lead to a great variation in their spectrum. The quality of artificial light will not be a major issue in case you are simply adding more light to a setting which already receives some amount of natural sunlight. On the other hand, if you are growing orchids only under artificial lights, the quality of light is vital. Orchids grow best under artificial lights when the different light sources are combined to complement each other, thereby producing a spectrum that is almost similar to sunlight. If the different sources of light are used separately, the light emitted by them will be entirely different from sunlight.
In order to compensate for what the artificial light sources lack vis-à-vis the power of sunlight, it is advisable that you keep the lights on for a minimum of 14 hours to 16 hours daily. Growing orchids completely under artificial lights offers especial advantage - you will never have a moment when it is cloudy. As a result, even the techniques involved in watering as well as culture will be less variable.
If you are thinking of using fluorescent light to compensate for the sunlight received by your orchids, you should know that the ordinary luminescent lights are not suitable for growing orchids as they radiate large amounts of heat. Since the source of artificial lights needs to be close to the plants, using this type of lights may actually burn them. Instead you will be doing the plants a favor by using fluorescent tubes, which not only cover a large area and also provide illumination, but also emit lesser amounts of heat in comparison to the amount of light produced by them. In addition, fluorescent tubes are also relatively cheaper and more efficient. This type of light is excellent for growing orchids requiring low lights. However, orchids requiring above 1,800 fc of light will not flower properly when grown under such lighting.
Irrespective of their variety, all fluorescent lights lack some fraction of perceptible spectrum. While the green and blue wavelengths of the regular cool white bulbs are higher, they are deficient in the orange-red spectrum which is vital for photosynthesis. Similarly, the warm white bulbs have more of the yellow spectrum, while they are deficient in the blue wavelength of visible light. In such situations, regular cool white and warm bulbs are not only relatively inexpensive, but also offer a good mix. In fact, they provide a solution to your lighting problems for growing orchids, as they apparently give sufficient proportion of all the wavelengths of the spectrum fulfilling most of the requirements of your plants.
Aside from the above advantages of using fluorescent tubes for growing orchids, they also last relatively longer. Even if you use cool white fluorescent tubes continuously, they will provide light for about 20,000 hours. However, their effective lifespan is significantly lower compared to their burnout time when used for horticultural purposes. When used for growing orchids, you need to replace the fluorescent lights after a year and in any case they should not be used continuously for over two years despite the fact that they may still continue to provide light. It is important to note that the middle of a fluorescent tube offers highest amount and, hence, the plants should be placed in the zone where the amount of light is higher. At the same time, you ought to know that the amount of light offered by fluorescent tubes is significantly less at their ends. You should never use short fluorescent tubes, especially those measuring about 2 feet, for growing orchids, because they are virtually useless for this purpose. These days a different type of fluorescent tubes called "power-twist" fluorescents is available and they offer 15 percent extra light compared to the regular ones, because their surface area is larger.
It is essential to use no less than four 40-watt fluorescent tubes for growing orchids. These tubes should be placed at a distance of 6 inches (15 cm) from each other. The orchid tops that are closer to the fluorescent tubes will receive the maximum amount of light. Ideally, you should position the plants no further than 8 inches from the fluorescent tubes. You can obviously place the plants even closer for more light, particularly at the ends of the tubes where the intensity of light is much less.
HID (high-intensity-discharge) lamps are considered to be the best type of artificial lights available for growing orchids. However, these lights are also most expensive. Such artificial lights comprise metal halide lamps, high-pressure sodium lamps and quartz tubes packed with mercury or sodium vapours under pressure and enclosed by phosphorus coated envelope with the capacity to absorb ultra-violet (UV) rays. In fact, HID lamps are highly efficient and offer superior quality spectral light. The only downside of these lamps is their extremely high price, which is attributed to their special features.
On the other hand, when you are using HID lamps over a long period, the low running cost can make up for the high amount of money you invest in the beginning. Almost all types of orchids will flower when grown under HID lamps, because they emit high intensity of light. For instance, a 1,000-watt HID lamp is able to emit as high as 12,000 foot-candles.
Compared to the sodium halide fixtures, metal ones are cheaper initially. Moreover, it is quite easy to convert the metal halide fixtures to hold sodium lamps, in case you change your mind later. However, you ought to know that metal halide lamps actually depreciate much faster compared to the sodium ones. When these lamps burnout they exhaust 50 percent of their power; while the sodium lamps just lose 20 percent of their power at this stage. It is necessary to replace sodium lamps once in two years, whereas the metal halide lamps should be replace every year.
It is worth noting that the red-orange-yellow spectrum of high-pressure sodium lamps is relatively high and, hence, they are preferred for orchids grown in greenhouses. However, the sodium lamps have a downside too - they emit a yellowish light, which is very unappealing and plants grown under such lights have a terrible pinkish-gray appearance. On the other hand, metal halide light is comparatively balanced and looks natural. Their blue spectrum is relative higher compared to the regular sodium lamps. These days, you can purchase a special type of sodium vapour lamps known as "agro-designed". These lamps have been particularly designed for use in horticulture. Compared to the general light, the blue spectrum of these agro-designed sodium lamps is 30 percent extra. Metal halide lamps give out about 125 lumens/ watt, whereas the light from sodium vapour lamps can be as much as 140 lumens/ watt. (Lumens actually denote the brightness of light available for each watt).
Before we conclude, it is important to mention that you need to be cautious while using water in the neighbourhood of HID lamps, because these hot bulbs may break or crack when droplets come in contact with them. It is also advised that you use a reflector with a view to keep the extremely intense HID lamps from directly shining in your eyes. You can also use a rotator to move the lamps continuously over the orchids, thereby making sure that there is an even lighting. At the same time, it will also help to avoid hot spots.