Light is one of the vital factors for growing as well as inducing orchids to bloom. Absence of sufficient light is said to be the main cause for an orchid's inability to produce flowers. Then again, excessive light is often a problem and it may cause sunburn. While some orchid species need total sunlight, there are others that perform well under restricted light. It is important to remember that while in the wild, orchids rarely grow in extreme light conditions or in places where ventilation is poor. However, you are actually lucky that you can provide your orchids grown indoors with the right amount of light they require. Adequate and proper light helps the orchids to remain healthy as well as bear exotic blooms.
If you are growing orchids indoors, it is possible to control the amount of light the plant receives. All you need to do is place the orchid close to a window. Preferably, you should place the orchid close to a window that is facing east or south. However, even placing the orchid close to a west facing window can be beneficial for the plant if you are able to soften the strong afternoon lights by putting up fine curtains. In fact, bay windows can prove to be excellent sites for growing orchids indoors. At the same time, to a great extent the solariums and skylights help to expand the indoor area receiving proper light for growing orchids. It is advisable that you carry out experiments to find the best location to grow orchids indoors. At times, moving the plant by only a couple of inch towards or away from the sunlight from the place it has been positioned to receive sunlight can prove to be a major difference for the plant - it can change a plant from merely existing to thriving well! During the winter months when the temperatures drop severely, it is advisable that you take the orchids to some distance away from the glass. Place a thin curtain between the glass and the orchids where there is even a light hint of sunburn. Alternatively, you can also move the plant away from the window or place it in any other location where the light is softer. However, move the orchids to a brighter spot or a window where there is more light if you find the plant developing deep green foliage or if they fail to bear flowers. In present times, windowsills are usually not very wide and, hence, they are unable to hold a potted plant. Nevertheless, you can widen the narrow windowsills by adding wider ledges to them or by placing a narrow table just beneath the windows to make enough room for your orchids. It is important to ensure that your indoor orchids do not grow too tall so that they become disproportionate with the window. Often it is said that a window plants should not grow beyond 30 inches (1 foot) in height. Usually, it is not very difficult to obtain a plant that is of this size or even smaller. You will find numerous orchid miniatures whose height is less than a foot. If you suspend two or additional shelves in a window it will have place for about 12 or more orchids. These days you can procure greenhouse windows that are sold as append structures that can help to accommodate more orchids. This is indeed a very tempting way to get extra space for your plants. However, while growing your orchids on modern day windowsills or next to them, you should bear in mind that the light available to your plants in these type of windows is stronger compared to the traditional windowsills. Hence, you will be required to give some additional attention and care in providing the plants with adequate shading as well as ventilation. If you can do this properly, your orchids will certainly flourish in such locations.
Often people ask what can be described as enough light. It is worth mentioning here that flowering plants require more light compared to those that are grown only for their attractive foliate. This is because the plants require additional light or energy as well as materials to bear flowers. This is one reason why you can grow orchids that have an appealing appearance, but do not bloom. These plants receive sufficient light for their survival, but not for bearing flowers. It is interesting to note that orchids will provide you the best indication regarding appropriate light. In fact, you will not require a light meter to read the intensity of light - the leaves of the plant will give you an accurate hint. When orchids are grown in appropriate light intensity, their leaves usually have a moderate to slight grassy green hue. On the other hand, when the intensity of light is poor, the leaves as well as the growth usually have a greener and deeper appearance. While this may appear to be a healthy sign, this means they do not receive enough light to bloom. At the same time, absence of adequate light means the orchid leaves will not be as glossy. They will not be shiny enough to reflect light. When the light conditions are very low, the orchids will be softer and have stunted foliage. In addition, their stems will be elongated and the distance between two stems will be more.
Generally, when orchids are grown indoors, they do not get enough light. However, the plants may be exposed to too much light when they are placed outdoors during the summer. In case there is an excessive heat build up, especially under direct sunlight, the leaves of the plant can burn and become blackened as in sunburns. Moreover, even if high intensity of light does cause sunburn, it may exhaust the plants' food reserves. Consequently, the flowers will starve and this will be manifested in the leaves color turning yellowish. At their maximum light endurance level, orchids usually develop a reddish tinge.
The light used for growing orchids is generally expressed as foot-candles (fc) of light. Actually, this term is the measurement of the light strength that falls on a surface. In other words, it is the measure of illumination or density of the light amount on a surface. Orchids are broadly classified into three light groups - low (1,200 fc to 2,000 fc), medium (2,000 fc to 3,000 fc) and high (3,000 fc and above). However, foot-candles do not evaluate the amount or duration of light at a place, though they both are vital for horticulture. On the other hand, foot-candles provide a guideline for the comparative requirements of different types of orchids, which helps to assess specific categories or types of light requirements. In fact, measuring the intensity of light by foot-candles (fc) is very helpful when you are evaluating the actual sunlight comprising the entire spectrum of light wavelengths, which is ideal for growing orchids. In case you are growing orchids outdoors in direct sunlight, you should not be concerned over the light quality available. The only thing that should matter to you is the sunlight's intensity. You can measure this in foot-candles with a photometer. The relative intensity of light can also be measured with a hand/ eye test. This system involves putting your hand between the source of light and the plant. The hand should be placed about 6 inches (15 cm) higher than the leaves and then you need to observe the shadow cast by your hand. If the shadow is sharp-edge it signifies that the relative intensity of light is high. On the other hand, a shadow with soft edge will probably mean moderate to low light for orchids. In case, there is no shadow at all, it means that the light is not sufficient for an orchid to bear flowers. On a very bright summer day when the sun is in its full glory, the foot-candles lighting up a surface outdoors is roughly 10,000. When you have an overcast sky during the day, the intensity of light will be about 1,000 foot-candles. Indoors the minimum intensity of sunlight may be very low (100 fc) or very high (5,000 fc) during noon on a clear day, provided you have placed your orchids close to a glass window. This intensity of light actually happens on June 21, when the Northern Hemisphere received the highest amount of light. Ideally, you should measure the intensity of light at noon on this day to find out the utmost foot-candles reaching the orchids that are growing in any specific location outdoors.
Apart from the amount of light, you should also be careful about the duration of light required by your orchids. In fact, these plants require a specific period of light intensity. Orchids that require maximum light actually flower best when they are provided with light for a full day - no less than six hours. Even orchids that require the lowest duration of light need their requisite light for the longest period possible during the day time.
Barring the equator, the amount and quality of sunlight varies significantly during the year in all places across the globe. While the amount of light is highest during summer, it is lowest during the winter months. Usually, the amount of light during summer and winter varies by a factor of 5 to 10 times. In addition, the amount of light also varies during different times of the same day. In such situations, you may find several windowsills ideal for growing orchids. If not perfect, you can of course adapt them to grow orchids, particularly if you keep the flowers near the glass. However, plants that are acclimatized to growing on windowsills receive different amount, intensity as well as extent of light at different times of the day and year. Usually, a south-facing windowsill is best for growing orchid. East, which receives most of the morning sun, is the next best location, while the west is the third preferred position, despite the fact that the westerly windows may become very hot as the plants will be receiving most of the afternoon sun. A north-facing windowsill is the least preferred position for growing orchids, because these are said to be very unfavourable for the purpose. However, a north-facing windowsill may also prove to be useful provided they also face reflective walls. Even if the walls are not reflective, they can be made reflective. Alternatively, you can make them further illuminated by adding light from artificial sources. If you are using glass for transmitting sunlight, ensure that you always keep them clean. At the same time, keep the orchids near the windows and purchase orchids that can adapt to the available sunlight. Also ensure that the leaves of the plants are always kept clean to enable them to absorb maximum sunlight available. Also arrange the plant in such a manner that the leaves of one plant are not overshadowed by those of other plants. The plants with artificial light whenever required also increase the duration of the artificial lights with a view to make up for the lack of power from sunlight. It is advisable that you also make the environment of the plants maximum possible light-reflective. Also use aluminum foils, matte-white walls, mirror tiles and similar things - preferably Mylar lining, which possesses the ability to reflect as much as 98 percent of available light.