Proper Lighting For Your Houseplants

Most houseplants are hybrids of plant species which grow wild, somewhere in the world. A good rule of thumb for keeping them healthy is to try to match the same environment from which they originated. You may not be able to match every criteria for your plant, but every small step you take to ensure the plants comfort will be a giant step towards keeping your friend healthy.

Proper lighting and watering are, by far, the most important criteria for the health of your house plant, but temperatures and humidity will drastically affect your plants as well. Generally, tropical plants enjoy a relative humidity of 50%-70% and warm temperatures. Unfortunately, when temperatures in the home rise above 67 degrees F., the humidity drops drastically, so it may be necessary to sacrifice a few degrees of warmth in lieu of an increase in the humidity.

Of course, there are always exceptions to the rule. Succulents being the most notable, which prefer warmer and drier conditions. At temperatures below 60 degrees, African violets will stop blooming, Poinsettias may drop their leaves, and the leaves of Gardenias may turn yellow. It will be a great benefit to your plant if you do a little research about what the needs of your particular species happen to be.

Light intensity refers to brightness and is measured in foot-candles, which is defined as the amount of light that one candle produces, measured one foot away. Outdoors, the amount of sunlight that is cast may be 10,000 - 12,000 foot-candles. Indoors, the amount of light that enters the room is only a small amount. While most plants will perform best with bright light conditions, some plants can tolerate moderate to low light conditions.

While light intensity is measured in foot-candles and can be evaluated by using a light meter or photographic exposure meter, you can also follow these general guidelines.

Low Light (75 foot candles)
North window: a few feet away; East/West window: 3-10 feet away; South window:15-20 feet away

Medium (average) Light (150 foot candles)
North window: directly in front; East/west window: a few feet away; South window: 3-10 feet away

High or Bright Light (300 foot candles)
East/west window: directly in front; South window: up to 5 feet away

Direct (1500 foot candles)
South window: directly in front

Keep in mind that light conditions change throughout the seasons. Several factors can influence your light intensity and duration. For example, the sun is higher on the horizon in the winter (increasing the brightness indoors) and lower on the horizon in the summer (decreasing the brightness indoors); surrounding trees and shrubs may block sunlight with their leaves in summer, but allow for more light during the winter after their leaves have fallen off.

Light duration refers to the number of hours of light that falls on a plant in 24 hours.

In low light conditions, plants can benefit from increasing the duration of light. Duration of 14 - 16 hours is sufficient. Do not expose plants to more than 16 hours of light since they need a rest period too. Also, be aware that flowering response in some plants is influenced by day-length and should be considered when supplementing the available light.

Light quality refers to the wavelengths of light. Plants need blue and red wavelengths for photosynthesis. For flowering, they also need infrared light.

Choosing lights

Incandescent lights: mostly red, some infrared, low blue

Fluorescent lights: vary according to manufacturer

Cool white: mostly blue, low in red

For foliage plants, using cool white fluorescent bulbs works well. For blooming plants, use incandescent or special "grow light" bulbs.

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