The amount of light an orchid receives is critical to its survival; however, it is the last factor people consider when they are experiencing problems with their plants. Usually they will blame the amount of water, fertilizer or heat as the culprit. Since many indoor plants can thrive on low light levels the orchid grower incorrectly assumes that their orchids work the same way.
If your plant is located in a darker place in your house it may do well for a week or two but after that you're inviting trouble. Indications that your orchid is becoming ill include thin, dark green new growth, sagging leaves and even brownish-black crown rot if water is allowed to stand in the “hollow” where your plant's new leaves are sprouting from.
So how much light does your orchid require and how much is too much? Also how do you measure the amount of light?
For optimum growth most orchids require as much light during the growing season as would be found under the shade of a large tree in direct sun, with absolutely no direct sun hitting your orchid plant. If your orchid is a Cattleyas or Vandas you'll need about the same light as would be found out in the open on a cloudy, gloomy day.
Too much light is usually to blame when orchid leaves turn a bright, whitish yellow, (or black and burnt if exposed to direct sun) but for beginners, too much light is hardly ever the problem.
So how can you know how much light your plant is actually receiving and how do you measure it? The value of the amount of light is expressed in ‘foot candles'. One foot candle is defined as the amount of light received by a surface lit by one candle one foot away.
How do you know how much light is coming in through that window? Since the perception of brightness is a subjective matter that varies with age-even gender-from person to person, the only way to really tell is to measure it, using a light meter. Meters that display brightness levels in foot candles, lux, and lumens can be bought at specialty stores and may be available through online sources. These meters can be expensive and you may not want to make that investment when you're just starting out. If you have an older, manual camera with a built-in light meter, you can use that to measure your light levels. Here's how:
Set the camera's film speed to ASA 200 and its shutter speed to 1/125 of a second. Aim the camera at a white sheet of paper placed where your orchid is growing. Get close enough so that the meter records only the light reflected from the paper: the paper must fill the viewfinder. Focus on the paper and adjust the lens aperture until a correct exposure shows on the camera's light meter. Once the exposure is correct, look down at the aperture setting on the lens. The F-stop reading will convert approximately into foot candles as follows:
F-stop – Footcandles
2.8 – 32
4.0 – 64
5.6 – 125
8.0 – 250
11 – 500
16 – 1,000
22 – 2,000
Most orchids that are grown commercially for sale require between 800 and 3000 foot candles of light to thrive and bloom. Since the amount of light available in the typical living room is between 30 – 80 foot candles it's easy to see why most novice orchid growers don't provide enough light for their plants. If your growing area is too dim, you can supplement your natural light with artificial light. Fluorescent fixtures and bulbs can be purchased very inexpensively at major home maintenance outlets. Grow lights can be used as well. For your efforts you'll be rewarded year after year with magnificent blooms and lush growth.
