Light Levels for Houseplants
In any case, knowing a plant’s native habitat can give us clues as to its care, and houseplants are no exception. A great deal of houseplants are native to the tropics, where the climate is most like the interiors of our homes: stable temperatures, never freezing, and with a range of light levels.
The roots of many of the houseplants that grow under tall trees are adapted for the humid, warm climate hidden beneath the trees. These plants thrive under the shade and in high humidity when the vegetation of these trees filters the sun. The closer you are to re-creating a houseplant’s native habitat, the better your chances of success. Consequently, you should try to replicate the sunnier, less humid climates of all the plants you intend to grow.
When given too much light or too little light, a plant is more likely to become infected, pest-infested, or prematurely die. However, finding optimal lighting can take some time and trial, so you’ll need to monitor your plant closely. Fortunately, most plants have information about their sunlight needs on the label.
Outside it’s often easier to determine how much sunlight you’re receiving than indoors, since you can see where the sun is hitting directly. Indoors, light can be more subdued. If you want to figure out whether a houseplant will do well in your home, you’ll need to know the different types of light you have.
Why do plants need light?
Light is crucial for plants in order to produce the food they need for growth and flowering. All living organisms depend on light to produce sugars, starches, etc. Plants are the only species that can harness the energy of light in order to make these substances.
Is light color important to plants?
Certain colors or wavelengths of light are more important for plant growth than others. Leaves reflect and derive little energy from the yellow and green wavelengths of the visible spectrum. In contrast, the red and blue wavelengths of the light spectrum are the most important energy sources for plants.
Plants growing outdoors, in greenhouses or close to windows are exposed to a balance of wavelengths of light from the sun, including the blue and red light that plants need. In settings where plants receive little or no natural light, additional light from artificial sources must be provided for adequate plant growth.
Relying on Window Light
The sun coming through the windows is often assumed to be sufficient for the houseplant, and it can be in some cases. However, light passing through glass isn’t nearly as strong as direct sunlight from the outdoors. In addition, unless your grow room is in a greenhouse, the light might change throughout the day depending on the direction the window faces.
The amount of sunlight that comes through windows is affected by other factors, including the size of windows, eaves and overhangs, and shading from trees and buildings. Because of the sun’s lower position, more direct sunlight usually occurs in winter; however, it is weaker in intensity, and there are fewer daylight hours than in summer.
How much light should plants receive?
The amount of light required for each plant varies, but most plants do not require much light with the light fixtures available for home plant lighting.
Generally, plants that can adapt to interior settings can be grouped in three general categories: those that require low, medium and high lighting intensities. Light categories generally indicate a minimum level of illumination. Growth is often best near the top of these recommended light ranges.
A foot-candle is a measurement of light intensity, or brightness, indicating how much light is received by a square foot of surface that is 1 feet from the light source. One foot-candle is equivalent to one candle.
Determining Indoor Plant Lighting
There are three main types of interior plant lighting:
Bright Light
It should receive a minimum of five or six hours of direct sunlight each day, preferably more, from southern or western facing windows. The winter can be challenging, but you must resist the temptation to move the plant closer to the window. When you move toward a window, the draft becomes colder, making it difficult for plants that require bright light to thrive.
Indirect Light
Indirect light can be found in places with an east-facing window, or in an interior of a room that receives full light from a south- or west-facing window. The light source may be covered by a sheer curtain, for example.
Low Light
Many rooms suffer from low light, especially in winter. Rooms with windows that face north or have partially shaded windows would qualify as low light environments. Low-light rooms can still support species of plants with artificial light. If you can’t easily read a newspaper, the room probably has low light.
What window provides the best light?
For best growing conditions, choose large windows and place plants far back into a room. The shape, size, direction, overhang, and shade provided by trees or nearby buildings also matter when choosing windows for plants. However, low-light plants rarely receive enough light at distances greater than 10 feet from an average window. The best window location for plants is one that is not shaded by a large overhang, trees, or other structures.
The brightest light conditions are provided by windows facing south. In winter, houseplants can benefit from the light coming from south windows. The bright light that shines through south windows may sunburn plants that don’t require bright light in late spring, summer or early fall. Plants requiring less light and indirect sunlight should be placed near a north window or to the side of a large south window at these times. South windows are the best choice for plants that prefer bright light and some direct sunlight.
West and east windows are well suited to plants in the middle light range, whereas north windows are only appropriate for plants needing lower light levels and should not receive direct sunlight.
Factors Determining Your Plant’s Position
When determining how much light your houseplant requires, it’s also important to consider the surrounding environment. There is no certain way to determine the right lighting level for houseplants, but keep these considerations in mind when selecting a location.
Temperature
It’s possible for plants in close proximity to a source of heat, like a heating vent, to be less able to cope with bright light than those in a cooler spot. When your plants seem to wilt even when you give them consistent water, they may need the heat source more.
Humidity
In the same way that low levels of humidity can make plants wilt, a lack of moisture can cause plants to become stressed as well. As a result, you can sometimes leave the plant in its optimal light conditions as long as it is misted regularly or has a nearby humidifier.
Duration of Sunlight
Plants generally need direct sunlight all day long. If your plant cannot be placed in a spot with ideal light conditions, you may need to provide supplemental lamp lighting.
Seasonal Changes
It’s not just the length of the days that changes as the seasons change. The angle of the sun is also different. For example, when the days are long and the sun is high in the sky, your western facing windows might get direct sunlight all day. In short days when the sun is low and only coming in at an angle, even a window facing west will not provide the plant with enough light.
How can I tell if a plant is getting enough light?
It is possible to determine whether your plants are getting enough light by observing their growth pattern. Poor growth may indicate insufficient lighting, but could also indicate other issues. If a plant doesn’t receive enough light, long internodes (the distance between leaves) or smaller leaves will develop, along with pale green stems and foliage, yellow leaves, and smaller leaves.