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How Do Indoor Plants Photosynthesize – Here’s The Process

Light and water are the two main requirements for plants to live. The soil they grow in is also essential, but no plant can live in complete darkness. Light is required for photosynthesis, converting light into energy and food the plant uses to grow. Outdoor plants get sunlight on their leaves, but indoor plants don’t. How do indoor plants photosynthesize?

Plants can use any available light in the room to photosynthesize; this includes sunlight and artificial light. Some indoor plants only need a small amount of light to trigger photosynthesis.

Now that you know how indoor plants photosynthesize, you may have other questions. Let’s dive in to learn more about photosynthesis, the light needed to trigger it, types of lighting, and much more!

What Is Photosynthesis?

Photosynthesis is a chemical process where light, carbon dioxide, and water are converted into glucose, and oxygen is released as the byproduct.

Chlorophyll absorbs light and converts it into energy for the plant to use. This energy is used to break up water and carbon dioxide molecules. It uses the atoms to build glucose and oxygen molecules.

The plant uses glucose for food, and the oxygen is released into the air for us to breathe.

We think of this process as requiring sunlight. But plants don’t need any sunlight to photosynthesize. The light can be from the light coming through a window, a table lamp, or a room’s available light.

You’ll need to learn the light requirements of your plants to know where you’ll be able to locate them in your home. You can use artificial lighting if you want a plant in a space with insufficient window light for photosynthesis to occur.

How Does Photosynthesis Occur Without Sunlight?

Outdoor plants receive direct sunlight, but indoor plants do not. How do indoor plants photosynthesize without sunlight?

The best light for plants is sunlight. It contains all the wavelengths of light: red, orange, yellow, green, blue, indigo, and violet.

Plants only need two of these light wavelengths: blue and red. Blue is for foliage growth. Red is for root growth, flowering, and producing fruit.

Most indoor plants only need a little sunlight to photosynthesize, with some needing no sunlight. Indirect or artificial light will trigger photosynthesis for these plants.

Some plants need sunlight, which should be placed in a window without any filters.

Is Sunlight Through a Window Enough for Plants?

Indoor plants vary widely in their light requirements, ranging from as little as 2-4 hours per day up to 12-16 hours, with most plants needing 4-6 hours of light exposure. 

Some plants need direct sunlight, and some are fine with indirect light.

What Is Direct Sunlight?

Direct sunlight is unfiltered light from the sun that hits the plant without any interference. Outside plants receive direct sunlight. 

The light through a south-facing window is called direct light by some gardeners, but most consider only the outdoor sun to be direct.

Large windows facing south provide the most light to indoor plants.

Due to diffusion and reflection, the intensity of the sunlight coming through a glass window can be reduced by as much as 50%. This can help prevent the plants in front of the window from becoming sunburned.

What Is Indirect Sunlight?

Indirect sunlight is when there is something in the path of the sun. This can be a sheer curtain, a tree outside, a window awning, or light reflecting off a surface. 

As mentioned above, most gardeners consider the light coming through the window glass to be direct sunlight, though the reduction in light is much less than from a sheer curtain.

Most indoor plants will thrive in indirect sunlight and will get sunburned if put in a sunny window.

Which Windows Get the Most Sun?

When planting indoor plants, it’s crucial that you know which areas of the home receive different amounts of light. That can have a huge impact on your plant’s ability to grow. I’ve broken them down in the chart below.

Window TypeLight Impact
North FacingThis receives small amounts of sun. Ideal for plants that need low shade such as Ivy And Snake Plant
South FacingConsistent light throughout the day. Late morning and Early afternoon provide the most opportunity for high-light plants. Plants with medium requirements work as well with a filter attached.
East FacingMostly an early morning distribution of sunlight. Great for medium-light plants.
West FacingMostly an afternoon light situation.

Light Intensity For Indoor Plants

A foot candle is a way to measure light intensity. It’s based on the amount of light that falls on a one-square-foot surface that is one foot away from a single candle.

The full sun outside is about 10,000–12,000 foot candles.

Here is a list of light intensity ranges and the plants suited for them:

  • 200–1000: This is a combination of very low light all the way to ordinary natural light in a room. Plants that require little light or tons of shade do well in this range.
  • 1,000–3,000: Quite a bit of light here, but its indrect. This is great for a plant that needs an extra bit of intensity, but not so much that the direct light negatively impacts it.
  • 3,000–5,000: The more intense light range, ideal for plants that need as much sun as possible without being placed outside. These are usually in the brightest rooms of the home with the largest windows. Mostly East or West facing.

Can Photosynthesis Occur in Artificial Light?

As stated earlier, photosynthesis can occur with any light, not just direct sunlight. This includes certain types of artificial light.

Grow light kits are available with light fixtures and reflectors, which are suitable for starting or growing plants. For houseplants, you can use any light fixture, including a lamp, as long as it uses a proper bulb and is placed, giving the plant the most benefit.

What Types of Lights Are Available?

There are different types of artificial light, and some are more suited to plants than others.

Fluorescent lights are the most economical lights to use. They’re available in tubes or compact bulbs (CFL) that can be used in regular lamp sockets. Regular ones are a good source of blue light, but not red, so look for ‘full-spectrum’ bulbs or use a combination of ‘cool’ and ‘warm’ bulbs. They don’t give off much heat.

Grow lights come in tubes and bulbs for lamps and contain the full spectrum of light. They’re suitable for plants that bloom, such as African violets. They’re more expensive than full-spectrum fluorescents and don’t give off much heat.

LED lights don’t give off a lot of heat and are energy-efficient and long-lasting. You need to use LED grow lights rather than ones for general use. They come in bulbs you can use in a lamp, tubes, bars, panels, a grow kit, and more. These are the most expensive option but are very popular.

Incandescent lights are a poor choice. They produce a lot of heat and are a good source of red light, but not blue light.

Halogen lights for plants provide full-spectrum light but, like incandescent lights, give off a lot of heat.

An economical way to provide light to your plants is to use one grow light tube with one or two ‘cool-white’ fluorescent tubes.

How Much Light Should Plants Receive?

Place the light 6-12 inches from the top of the plants. Especially for tube lights, the height of the light should be adjustable to accommodate the plant as it grows. Fluorescent and grow light fixtures are usually hung on chains with S-hooks to make this easy.

Most plants need 16 hours of light per day. It’s easiest to use a timer to turn the lights on and off automatically. Have the lights off at night.

Have the plants spaced so that they are not shading each other.

Final Thoughts

Many people love to have houseplants in their homes. However, their plants do not always thrive. One reason for this is insufficient light for the plant to photosynthesize. Photosynthesis is essential for plants to survive and be healthy. It’s the method they use to give themselves enough energy and food.

You’ve learned that there are more choices for giving your plants light beyond windowsills. You can select from various artificial lighting options to increase the light available to trigger photosynthesis. With these options, you can have a wider variety of plants and ones in rooms that used to be too dark for them.