The light needs of houseplants vary greatly and many are particularly sensitive to direct sunlight. But is light coming through a window considered direct sunlight or not? Let’s find out together.
Is light coming through a window considered direct sunlight? Light passing through a window is not direct sunlight because some of the light is scattered and reflected as it passes through the window, reducing its intensity. Light through a window is the most direct form of light available indoors, but is typically at least 50% less intense than direct sunlight outdoors.
Good lighting for your indoor plants is essential to ensure their healthy growth, but you don’t want so much light that it causes them problems. Read on to find out how much light shines through a window.
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How strong is the sunlight in my bedroom?
It’s amazing how much the light levels in your home vary. A plant a few feet from a north-facing window often receives only 1% of the outdoor light of a plant in full sun. With such a range of light intensity, it is important to place indoor plants correctly.
Here are a few examples to illustrate how light levels vary depending on where you place your indoor plants.
- deep shadow: (500-2,500 lux, 50-250 foot candles) Away from a north-facing room window: Most plants will have problems, but plants like cast iron plants, snake plants, and Chinese evergreens tolerate these low light conditions.
- Little light: (2,500 to 10,000 lux; 250 to 1,000 foot candles) Natural light on a clear day a few feet from an east-facing window. Most shade-tolerant houseplants do well.
- Bright and indirect light: (10,000 to 20,000 lux; 1,000 to 2,000 foot candles). Many houseplants will thrive in these lighting conditions. A south-facing room, away from direct sunlight, will usually have bright indirect light.
- Direct sunlight indoors: (20,000 to 50,000 lux; 2,000 to 5,000 foot candles). Many flowering houseplants thrive in these light conditions. A plant on a south-facing windowsill receives this amount of light.
- Direct sunlight outdoors: (40,000-130,000 lux; 4,000 footcandles+). Generally more than twice as intense as direct sunlight through a window. Plants that are moved indoors to outdoors often need to acclimate to increased light.
Why isn’t light coming through a window as strong as direct sunlight outside?
If you are outdoors and the weather is cloudy, rays filtered by clouds are not considered direct light. Likewise, if you are under a tree, light that hits you through the branches and leaves is not considered direct light.
The same concept applies to sunlight streaming through a window. The light passes through the glass barrier of the window and therefore loses part of its luminous intensity and energy. Light is refracted, some is reflected and some is scattered, which reduces the intensity of the light.
Like a rainbow, sunlight is made up of rays of different colors. When these rays are together, they produce sunlight at its full potential. When light passes through something, be it a cloud or a window, it loses some of its power, either by reflection or by scattering.
Different types of light through a window.
There are different intensities of light filtering through a window. Each of these lights depends on the location of your window and any barriers between the sun and your window, both inside and out.
Square
When we talk about location, not only the direction of the window is important, but also the influence of different seasons. The amount of light and the intensity are different in the warmer months than in the colder months.
north-facing windows
North-facing windows never receive direct sunlight through them due to the path of the sun, which rises in the east, crosses the southern half of the sky, and sets in the west. A north-facing windowsill is suitable for shade-tolerant plants, and away from a north-facing room window, only very shade-tolerant plants will thrive.
I wrote an article on 21 plants that are ideal for growing on north-facing windows. You’ll be surprised how many tall, beautiful houseplants love north-facing rooms and thrive in low-light conditions.
If you really want to grow light-hungry plants in a north-facing room, try placing them as close to the window as possible or consider using a grow light to increase light levels, especially in winter.
south facing windows
These are usually the warmest and brightest places in the house. The intensity of the light is felt throughout the day because the sun always shines in this part of the house. Either early in the morning when the sun rises or in the afternoon when the sun goes down.
Most plants grow well in south facing rooms. Light-loving plants like cacti, many succulents, mildew spurge, citrus fruits and anthuriums can work well on south-facing windows. Move low-light houseplants away from the window and provide shade to protect them from direct sunlight.
east-facing windows
This is the best place in the house for plants that need morning or mid-morning sun, as it is the first place that receives morning light. This area is also generally cooler as the sun moves west.
East-facing windows are ideal for a variety of indoor plants. They get some direct sunlight in the morning, but avoid hot direct sunlight in the middle of the day.
west facing windows
This is the area that receives the most light after noon and it is also the hottest part, as the sun continues to shine in this area from noon until sunset. So if you have plants that need a lot of light, this is also a great place for them.
I like to keep plants that like light conditions on west facing windows. They avoid the strongest direct sunlight, but still get plenty of bright light.
Barriers
These can be of two types; inside or outside, and both do exactly the same thing. They filter direct sunlight and convert it into indirect light.
- interior barriers: Windows, blinds, curtains and the furniture itself are barriers that block all or part of the light that reaches your plants.
Using barriers to your advantage allows your plants to get the perfect amount of light. Placing a curtain in front of a south-facing window, or placing a plant in the shade of a piece of furniture, allows you to modulate the brightness from unbearable to perfect.
- External barriers: There are many external barriers that are easy to find in nature. These can be anything from trees to clouds to a gazebo.
Any of these natural elements that prevent sunlight from directly hitting you or the plants are considered an exterior barrier. These are less adjustable, but you still need to consider this when assessing your room, ideally before choosing which plants to place in your home.
Why is light intensity important for indoor plants?
Plants need sunlight to be able to use their natural process of photosynthesis. Plants need sunlight to convert carbon dioxide and water into plant food, sugar and starch. Without sunlight, plants can only survive for so long. Read my article on the ability of plants to survive without sunlight to learn more.
Not all plants need the same amount of sunlight. Some plants need more sun like many flowering plants. While many green leafy plants need less sun. So, knowing what kind of light your plant needs will help you maintain it.
One more thing to keep in mind: Most people like to choose a plant they like for their home or office and then choose a location for that plant in their space. It is much better to do the opposite.
First choose a place where you want your plants, then choose a plant. This way you will know exactly how much light is entering that spot. When it’s hot, when it’s dark, when it’s light, etc. All of these factors will help you determine the best plant for that area.
This, in turn, will help ensure that you take good care of this plant so that the plant not only survives, but thrives.
Last word
Light entering through a window is significantly less powerful than direct sunlight from outside. Most houseplant care guides refer to light streaming through a window as direct sunlight. Despite the reduced intensity, it can still burn your plants if exposed to direct light from that window.