How Do Indoor Plants Photosynthesize?

Golden Pothos

It is a well-established fact that plants need light to maintain proper health, but this becomes confusing when we think about indoor plants. Photosynthesis is a complex process that can have some surprising components that go far beyond basic sunlight; even plants that are kept indoors and receive no sunlight can convert light into energy. If there is no natural light indoors, how can indoor plants photosynthesize?

Indoor plants photosynthesize by converting any available light source into chemical energy. It is a misconception that plants must have sunlight in order to photosynthesize, and any light source is enough to start the process of photosynthesis since this triggers chemical reactions. 

Since photosynthesis has many biological steps that are the same for both indoor and outdoor plants, this article will explore how indoor plants are able to photosynthesize with minimal sunlight or no sunlight at all. 

Warning: It’s about to get really nerdy below. Adjust your pocket protector and continue reading.

Photosynthesis 101: An Overview

We all learn about photosynthesis in elementary school–but it never hurts to revisit the process to better understand how indoor plants achieve photosynthesis without complete sunlight. 

That is the first misconception when it comes to photosynthesis: plants do not have to have direct sunlight to photosynthesize; in fact, plants do not even need sunlight at all to convert light to energy. 

This is because photosynthesis is triggered from any available light source, be it sunlight or a basic lamp next to an indoor plant. It can be hard to reconcile this fact since we were always told growing up that plants need sunlight to grow. 

Light is only one part of a four-part process in photosynthesis; therefore, to better understand exactly how the process occurs, let’s take a look at each part in detail. 

Light Absorption

Light, along with water and soil, are three components that plants need to thrive. Water cannot promote plant growth without light, which is absorbed through a plant in photosynthesis. As light hits the exterior of a plant, the light attaches to chlorophylls, which are attached to protein membranes within the leaves and stem of a plant.

The captured light is then transferred into energy, which is then used to remove electrons from water. 

The Transfer of Electrons

These new electrons are then transported throughout the plant until the electrons meet a new electron acceptor where the transport of electrons is coupled to the movement of protons from the stroma of the membrane to the thylakoid lumen, forming a pH gradient across the thylakoid membrane.

In simpler terms, this is essentially where the newly converted electrons create a force of sorts between the newly converted energy provided by the electrons.

ATP Production

Now that the electrons have been converted to energy, new energy-carrying molecules known as ATP (adenosine triphosphate) that can travel more widely throughout a plant to power all of its functions properly. Each living thing needs ATP compounds to cause the proper chemical reactions from a nutrient source, which in the case of plants, is light. 

Carbon Conversion

While the above three processes occur during the absorption of light, the final stage of photosynthesis can occur with or without light, which is one of the primary phases of photosynthesis seen in indoor plants: carbon conversion. This phase involves all of the electrons and molecules generated from the first three phases producing nutrients that are transferred throughout the plant. 

Photosynthesis is a complex process, but the simplest way to remember the process is to think of light as a form of food for plants. Light is needed to provide the processes that create nutrients and is just as vital to plant growth as water. 

Now that you have a better understanding of photosynthesis as a whole, let’s explore how this can occur for indoor plants that receive minimal or no sunlight at all. 

Take a look at this video for a great overview of the process of photosynthesis:

How Much Light Do Indoor Plants Need to Photosynthesize?

Without light, plants will die, and this fact is also true for indoor plants. Chlorophyll is unable to be produced if a plant is not exposed to light, which means that the plant will turn to either white or yellow before dying. Additionally, a plant that lacks light will develop an overlong stem in the process of trying to branch out to reach a light source. 

With this in mind, it may sound surprising that only a brief exposure to light can activate photosynthesis within a plant. It is also important to remember that plants also need carbon dioxide and water for photosynthesis to occur; light is the main component, but those two factors are necessary as well. 

When it comes to how much light an indoor plant needs to photosynthesize, this can vary depending on the species of plant. Since indoor plants can fall into the category of plants that need shade to survive, you can be assured that photosynthesis can occur in as little as 2-4 hours of light each day.

To be on the safe side, you can leave an indoor plant near a lighting source and not put the plant directly under the light. 

As long as the light is near the plant, the rays will reach the exterior to activate the process of photosynthesis. 

How Do Indoor Plants Photosynthesize Without Sunlight?

Sunlight is definitely the best source of light for plants. Since sunlight contains yellow, red, blue, indigo, violet, orange, and green light—you will never have to worry about a plant not receiving any required light spectrums to adequately grow. 

With this in mind, plants only require two light spectrums to grow: red, which promotes budding, and blue, which promotes growth. The intensity of the light and the length of light absorption can also be important depending on the type of plant.

When it comes to common indoor plants, intensity and duration are not as important since these types of plants have evolved to find unique ways to photosynthesize when light is limited. 

There are many factors that go into how indoor plants can survive without sunlight, so let’s take an in-depth look at each variable.

Types of Indoor Plants

Before we get into ways that you can add supplemental, effective artificial light sources to feed your plants, let’s talk a bit about how even small amounts of sunlight can trigger photosynthesis in indoor plants. Plants do not have to have direct sunlight to survive, which is obvious since plants would die off during the evening hours if this were the case. 

Most plants need only 4-6 hours per day of sun exposure, whereas other plants can survive completely in the shade and photosynthesize with only brief reflections of sunlight when the shade wears off. With this in mind, this is the reason that indoor plants have the ability to photosynthesize since these types of plants require very little sunlight to trigger the process. 

Let’s take a look at few common indoor houseplants and the light requirements of each. 

  • Rubber Plant. A rubber tree plant is certainly one of the more popular indoor plants due to the low maintenance required with this species. Rubber plants require no sunlight to actively photosynthesize, and bright, fluorescent light (more on this below) is more than enough to trigger photosynthesis. 
  • Money tree. The money tree is also a staple of indoor foliage due to its rumored ability to bring economic fortune to its owners. Money trees also require no sunlight, and bright lighting that is pivoted slightly away from the plant is enough to trigger photosynthesis during the day or night. Be sure to leave the light on for at least 4-6 hours. 
  • Palm plants. Palm plants, such as the bamboo palm, are a signature decorative type of indoor plant that is very popular. Palm plants are another great example of a plant that requires no sunlight to photosynthesize. Just be sure to shine a light near the plant but not directly upon it to avoid burning and discomfort. 
  • A string of pearls. This indoor plant is well-known for its distinctive oval leaves that grow rapidly in a vine fashion. Strings of pearl are also a type of indoor plant that needs lots of artificial light, but photosynthesis is best observed if the plant receives the light in an indirect fashion. 

These are just a few examples of indoor plants, and the one trait that you have probably noticed more than any other is that indoor plants do not really need sunlight to undergo photosynthesis. 

It is important to keep in mind that there are some types of plants that need some sunlight to grow properly, but most indoor plants can survive without it, so let’s take a look at how supplemental lighting sources can trigger photosynthesis. 

Lamp and Plant

Supplemental Lighting

Remember how plants can grow without sunlight with only artificial lighting? This is definitely true, but there are some types of light sources that are better for plants than just a standard light bulb. Let’s take a look at a few.

LED Lights

LED (light-emitting diode) is by far the most popular artificial light source for indoor plants. LED lights do not produce as much heat as other artificial light sources such as regular light bulbs. 

The brightness of LED lighting is also very strong without being too harsh. LED lights also come in many varieties, including as a screw-in replacement for lamps or, as a targeted, high-intensity greenhouse model that can suspend directly above indoor plants. 

What makes LED lights a great alternative for indoor plants is that these lights can provide a full light spectrum, much like sunlight. Since most plants do not need all of the spectrums found in sunlight, you can also tailor some strands of LED light products to only provide specific spectrums based upon the lighting needs of the plant.

Additionally, many LED light can also be programmed to brighten or dampen in intensity if the plants have light sensitivity. 

Incandescent Lighting

Incandescent lights are good options for supplemental lighting; however, the results are typically targeted for only a few different types of indoor plants that respond well to the heat levels this type of lighting can emit. Incandescent lights are primarily low in intensity when it comes to brightness, which means the main focus when it comes to plants will be warmth in favor of light. 

Any type of fern or vine-type plant responds well to incandescent lighting, but this type of light is not recommended for indoor plants that need large amounts of light. 

Fluorescent Lighting

Fluorescent lights are ideal for indoor plants since the intensity of the light is typically in the medium range between what most indoor plants need and what would be considered too harsh. This type of light provides a targeted approach to providing a perfect beam of light without having to fill large spaces.

Fluorescent lights also provide full-spectrum lighting in addition to a range of warm and cool tones in contrast to the harsh output of incandescent lights. 

This is what makes fluorescent lighting so popular in greenhouse settings because the light is strongly targeted to the surface of the plant exterior while not being too bright or overly warm; the balance is just right. 

Fluorescent lighting is ideal because it provides a perfect balance on the lighting scale, which is measured in kelvins (K). Kelvins are used to measure absolute temperature in a range of objects, including light. 

When it comes to light, kelvins are used to measure the visual warmth of a stream of artificial light, which means that the whiteness of the light translates to a ‘cool’ glow, whereas if the kelvin measures a red or warm temperature, the light is warmer than it is cooler, which can commonly be seen in incandescent lighting. 

Fluorescent lights have a high kelvin measure typically in the 6500-watt range. This means that the light is intense but not overly warm. Warmth is sometimes important for plants during the winter season, but most indoor plants will not necessarily need overly warm temperatures in conjunction with light. 

Of course, you can skip the need for artificial lighting if you choose to provide your indoor plants with minimal sunlight during the day. This can be achieved by placing the plants near a window to receive a few hours of sunlight to trigger photosynthesis. Another question to consider is how much light is too much light when it comes to indoor plants. 

Prayer Plant

Light Requirements for Indoor Plant Photosynthesis

Since light requirements are directly correlated to each individual type of plant, the amount of available light is only suited to the types of plants that need actual sunlight to survive, which can include many types of outdoor plants that you would like to try and grow indoors.

Since this issue is probably due to a lack of yard space in an apartment dwelling, you will want to choose rooms that are brightly lit with larger windows. 

If this is the case and you have a plant that needs sunlight, be sure to place the plant directly in front of the sunlight with no shade or objects blocking the rays of the sun. If your apartment has multiple rooms, it is important to remember that the brightest light comes through the window facing south, so be sure to place your plant in this window if available.

Plants that need sunlight will need the rays to shine directly on the leaves and stem. 

For all other types of indoor plants, you can resort to artificial light sources to activate photosynthesis. The true light requirement for plants to photosynthesize indoors is based on the light spectrum and light intensity to activate the chlorophylls within the plant. Plants contain both chlorophylls a, which absorbs both violet and red light, and chlorophyll b, which absorbs blue and red light. 

This means that there can be a wide range of deficiencies when it comes to artificial lighting. Plants need a certain type of light intensity to achieve photosynthesis, which is known as the light compensation point. This process is directly related to the point where carbon dioxide that is absorbed is compensated by the amount of carbon dioxide released.

The intensity of the light source makes up for the release of oxygen from the plant. 

The greater the intensity of the light source, the greater the rate at which photosynthesis can complete. This is why LED and fluorescent lights are ideal because there is a strong concentration of energy released into the light beam as opposed to the energy mostly coming from the heat of red and warm light–as seen with incandescent lighting. 

When it comes to indoor plants, getting the full spectrum of lighting from the sun is not always an option; therefore, you will need to make sure to provide blue and red light at the bare minimum. Let’s take a look at each color in relation to photosynthesis. 

Blue Light

Light is primarily composed of red, blue, and green in its simplest breakdown. Since green is not effective for plants and simply bounces off of the green leaves due to the chloroplasts within the plant, that leaves blue and red. Blue light is by far the most important light color for plants as blue light promotes chlorophyll production.

Much in the same way that the human body needs certain nutrients for healthy blood, the same is true for blue light and plants. 

Most types of chlorophyll can use the blue spectrum of light more efficiently than the red and far-red spectrums of light. More of the blue end causes the cells to be elongated, changing the growth pattern of the overall plant to a more compact size with the nodes closer together. This maximizes the space used and light available for each leaf in the growing area.

Blue light is important to plant growth and the proper function of plant processes. 

Red Light

If the blue light is responsible for the growth of plant parts, then red light is responsible for plant development such as seed germination, the growth of roots, and the budding of flowers. Red light is responsible for the overall appearance of a plant, which is a major cause for the appeal of plants overall to people.

A plant can be generally healthy and grow well with only blue light, but red light is essential if you want a plant to maintain a healthy appearance. 

To get the maximum amounts of blue and red light needed for proper photosynthesis of indoor plants, always choose LED or fluorescent lights due to the primary inclusion of red and blue light.

Light Direction

Since the sun is always at a perfect angle for plants to absorb its rays, indoor plants will need different directions to maintain the optimal light intensity for sustained growth and development. 

You will have to monitor this by making sure that the leaves are not wilting or changing color, or to check that the stems are not thinning out; if you notice any of these occurrences, it is likely because the plant is receiving too little or too much light. 

For indoor plants that need low or medium levels of light, one or two fluorescent lights that shine near the plant but not directly on the plant are optimal. Since photosynthesis can be activated from any part of the plant (leaves are best), the light will be able to reach the plant but not potentially cause drying or burning of the leaves. 

You will have to maintain a careful balance with this factor; there is no real way to ensure your indoor plant is getting too much or too little light than to watch how the plant appears over the span of a few days. If the leaves look withered or the stem appears thin and reaching towards the light, more direct exposure is recommended.

If your plant appears bleached or scorched, this is a sign of too much light, and distancing is recommended. 

How Do Indoor Plants Photosynthesize With Little or No Light? 

Plants cannot photosynthesize in continual complete darkness. Although it may sound odd to imagine, indoor plants can fully sustain themselves on what we would refer to as invisible light. Plants actively seek out both red light and far-red light, even though blue light is the most beneficial to plant growth.

A similar scenario would be how people crave sweets, even though lean meat and vegetables are the most nutritious food sources. 

Far-Red Light

Far-red light, when added to blue light, can increase plant growth by a substantial margin; therefore, plants that may be lacking in the light will seek out red light sources and reflect more far-red light, which is made even more competitive if there are other plants in the area. It sounds confusing–but plant photoreceptors can mimic this behavior if there is a major lack of available light in an area. 

A deficiency in blue light and an increase in both red and far-red light, therefore, creates nutritional imbalances in a plant, and abnormal growth and development will be stalled and potentially lead to death. 

This is the normal pattern for plants that need adequate light, but when it comes to indoor plants that truly need very little light to photosynthesize, just minimal amounts of both blue and red light can be enough to achieve the process. 

Light and Dark Phase

Photosynthesis has both a light and dark phase; therefore, it only takes a small amount of light to activate photosynthesis, and in the case of indoor plants that need very little light, this will be enough. During the dark phase of the process, the chemical reactions involved take center stage.

Therefore, if a plant only receives a small amount of light–the process will cycle through, which means a plant will receive some nutrition–but not enough. 

An Indirect Approach

Finally, there is a process where the available light can have an indirect approach to the process of photosynthesis. If you have your indoor plants away from a light source, either an open window or an artificial light, the light can be reflected from a number of different objects within the room. This is actually optimal because this ensures that the plant is not receiving far too much direct light.

Always be sure to check the plant guidelines to ensure that the plant needs low, medium, or direct light to maintain proper health. As long as the light is nearby and sustained for at least 4-6 hours, your indoor plant will photosynthesize. 

Final Thoughts

Photosynthesis may sound like a simple process, but the process can become complex based on light patterns and the individual needs of the specific plant. Indoor plants photosynthesize just the same as outdoor plants, and artificial light sources, granted the source or sources provide blue and red light, are perfectly fine to allow indoor plants to achieve photosynthesis. 

Always keep in mind that even though indoor plants usually do not need much light, you still have to monitor the light intensity from time to time to make sure that is right with your indoor plants.

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