Understanding Light Requirements for Indoor Plants
Your indoor lighting needs will have a direct impact on your houseplants’ growth and health. Not enough natural light or too much can cause them to look sickly, not to grow and bloom, drop leaves or die altogether. Light requirements for indoor plants are discussed in this guide, along with ways to provide the right amount of light and how to resolve lighting problems.
To learn more about how plants utilize light, what lighting in your home you can use, and how it can help them grow, continue reading. You will learn how to maneuver your plants around the home to meet their light requirements and also how to choose plants that will thrive at home under the lighting you have already.
Understanding How Light Affects Plants
Photosynthetic plants use sunlight, water, carbon dioxide, and chloroplasts to absorb the sunlight and convert it into food. Photographic plants are composed of chloroplasts, organelles within the cell, that perform photosynthesis.
These chloroplasts enable plants to adapt to changing lighting conditions by changing their distribution and number. Plants generally respond initially to lower light by increasing their chloroplast numbers. As a result, plants’ leaves often become darker green due to the increased need to capture more of the light.
As lighting levels increase, the number of chloroplasts can be reduced, and they will change where they are distributed in order to reflect less light, usually resulting in paler green-colored leaves.
Plants are not able to adjust to light changes very well, and each species has a maximum and minimum lighting level that it can tolerate. In addition, plants must adjust slowly to sudden changes in lighting, so sudden changes can be damaging to their health.
Factors Involved In Lighting
Lighting for houseplants is influenced by a number of factors. There are numerous factors to consider, including the direction of your windows, the intensity of sunlight that filters through, changes in lighting throughout the day, and what effect the weather has on lighting, too.
Your home’s orientation will determine the amount of light that your plants receive, so you should know which direction your home’s windows face so that you can determine what amount of light your plants will get.
If you are in a higher or lower latitude, you will have to adjust for variations in natural sunlight. Since the amount and timing of natural sunlight depends on the location of the sun on the horizon, higher and lower latitudes will have to take this into account. Likewise, mountains, hills, valleys, woods, and buildings may also influence the angle at which the sun strikes your windows.
The Direction Of The Windows
You should expect the lighting in east-facing windows in the morning and west-facing windows in the late afternoon and evening, since the sun rises and sets in the east and west, respectively.
On the northern hemisphere, windows that face south receive the most direct sunlight, while those facing north receive minimal direct sunlight. There are, of course, differences in the southern hemisphere, where windows facing north provide the most direct sunlight and those facing south the least.
We assume that you live in the northern hemisphere throughout the rest of this section.
In general, windows facing south will have the most sunlight available as long as they are not shaded by trees or other structures. A spot in your home in which you receive the brightest and strongest light is optimal for those plants that require ‘direct’ sunlight in the indoors.
While west-facing windows receive less intense sunlight than south-facing windows, they still receive direct sunlight for a portion of the day, in the afternoon and early evening.
Western windows will receive more indirect light in the early morning and early afternoon. The afternoon sun is intense and can increase the temperature near the window, so be careful with plants that could scorch easily and move them a few feet away from the window.
Early morning sunlight hits east-facing windows, making them a good choice for plants that require bright indirect light. These windows will then get indirect light through the afternoon, avoiding scorching heat.
Oriented northward, north facing windows receive the least amount of light, from direct sunlight. These windows are best for plants that do not require much light, such as ferns. For most plants requiring bright, indirect light in the summer, light from a north-facing window is usually adequate. As the light level decreases rapidly when you move away from the window, locations farther from the window work best for low light plants.
Plants that require low light in winter may thrive on a north-facing windowsill, but other plants may need to be moved to a higher light location, or you may need to use an extra grow light.
How To Make Light Less Intense
Houseplants can be given lower levels of light if they are located in a south-facing window. You can tone this light down by filtering it.
Window Sheers. Sheer curtains are lightweight curtains that will help block out some of the light coming through the window.
Window Films. Depending on the filtering level, window films block out varying amounts of UV rays; this is especially helpful if you have plants that are sensitive to the harsh summer sun.
Placement. In addition to moving your plants away from the window, select a room in the house that gets bright indirect light to avoid the direct rays.
Three other factors can also be considered when selecting lighting for your plants:
Intensity is best measured in foot candles. Light intensity reflected from a surface is crucial for houseplants. Foot-candles are the amount of light that falls on a flat surface closer than one foot from a single candle. Light intensity can also be measured in Lux (1 foot-candle = 10.764 lux).
Full Sun – (40,000–130,000 lux; 5000 foot candles+). All else being equal, direct light outside is about twice as bright as direct light indoors. This level of lighting is not possible indoors due to glass windows, which reduce the light’s intensity.
Direct Light Indoors – (20,000–50,000 lux; 2,000–5,000 foot-candles).
If there is direct light indoors, it is considered to be light that falls directly onto a surface and has passed through a window. It feels warm to your skin and produces distinctive shadows. Direct light indoors is considerably weaker than direct sunlight outdoors, at about 2000 to 5000 foot-candles. In spite of glass filters, direct indoor light can damage many indoor plants unless they have been specifically bred to tolerate direct sunlight. Many succulents and cacti flourish in direct indoor light.
Bright Indirect light – (10,000–20,000 lux; 1,000–2,000 foot-candles).
The term bright indirect light refers to the kind of light that isn’t directly reflected by the sun. This equates to about 1000 to 2000 foot-candles. Even when indirect lighting is blocked, it will cast a shadow, although its edges will be fainter and less well-defined. The indirect light in south, east and west facing rooms can be achieved by adjusting the distance between plants and the placement of them within the room.
Medium Light – (2,500–10,000 lux; 250–1,000 foot-candles). Imagine standing a few feet from a window in an east-facing room on a bright day and looking at the light emanating from it. Many foliage houseplants such as Calatheas, Philodendrons, Alocasias, Dracaenas will grow and do well in medium lighting.
Low Light – (500–2,500 lux, 50–250 foot-candles). Away from the window of an east- or west-facing room, or within a few feet of a north-facing window: Bear in mind that most people can read comfortably in a location providing only 25 foot-candles of light, so what is considered “low light” may be brighter than you think.
Very Low Lighting – (<500 lux, <50 foot-candles). It will seem dull, and even lighting only a few feet from a window can fall below the very low range. Snake plants, Cast-Iron plants, Chinese Evergreens, etc. will survive, but may not thrive under very low lighting.
There can be changes in the number of hours of sunlight per day depending not only on the season, but also on over a dozen other factors. You might only get a limited amount of good quality lighting per day depending on the size of your window or external obstructions.
If you intend to place a plant in a room, make sure it receives sufficient light throughout the day by examining the room at different parts of the day.
How Lighting Changes Throughout the Day
The amount of light that comes through the windows changes with the sun’s position in the sky. By contrast, a south-facing window will be filled with light all day long. A window facing west will be directly exposed to the sun during the afternoon, but indirectly during the morning and early afternoon.
In the morning, the sun shines directly on an east-facing window. Once the sun is no longer as hot, it takes on indirect sunlight in the afternoon. A north-facing window doesn’t receive any direct sunlight.
Seasonal Lighting Changes
Light coming in through your windows will also change with the seasons. In the summer, because of the earth’s position in relationship with the sun, its rays are more intense and last longer.
For example, in summer, your windows will be filled with brighter and more intense sunlight for a longer period of time, while in winter, the day will be shorter with fewer hours of daylight and less intense light.
Depending on the season, you may need to move your plants to a different location. For example, a plant that thrives in a western-facing window may need to be moved to a southern-facing window in the winter.
Furthermore, plants that thrive in a south-facing window in winter may suffer in the summer due to the intensity of the sun. If this occurs, it would be better to move the plant away from the window or into a window that faces west or east in the summer where it will receive less intense light.
North-facing windows are rarely ideal for plants during the wintertime, but shade-loving plants can thrive there in the summertime when the sun is brighter for longer periods of time.
Lighting Changes Due To Weather
If the weather is bad, sunlight will not shine in your home. Overcast, cloudy, or rainy weather will prevent sun rays from entering your home. Even plants that require direct light indoors will be safe for several weeks without negative effects of poor weather.
Winter is a harsh time for houseplants and many will go dormant due to a decrease in sunlight hours. If you live in an area with long, harsh winters, you may want to add supplemental lighting or move plants to another window so they can receive enough light.
Will A Plant That Is Meant To Have Bright Indirect Light Tolerate a Few Hours Of Direct Sunlight?
Usually plants that require bright indirect light will not scorch if exposed to no more than 1-2 hours of direct sunlight each day. However, some delicate houseplants, such as calatheas, can scorch if exposed to even a few hours of direct sunlight.
You may still be able to save the plant before it is severely damaged by placing it in excessively bright conditions, as they may turn pale before they scorch. Yellowing of sun-exposed or young leaves should be on your radar first. If you suspect excessive lighting, relocate the plant to a less bright location or take steps to protect it from harsh lighting.
When you move the plant farther from the window, the light rays are spread throughout the room. The sun’s rays are more intense when the plant is located near the window.
Plants with low light requirements can be moved farther away from a window. Using a light meter across the room will help you determine which parts of the room will receive the most foot-candles so you can place your plant accordingly.