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The Science Behind Indoor Plants and Sunlight: How Much Do They Need?

Posted on February 14 2021

The Science Behind Indoor Plants and Sunlight: How Much Do They Need?

Direct, indirect, diffused, dabbled, partial, and full sunlight. Is your head spinning yet? If not, you can always add North, South, East, and West facing windows to the mix! Even with the perfect amount of research, your dream plant may still decide it hates your house. You frantically look up information online, get conflicting advice, relocate your plant every other day, and finally decide to give up. Low and behold! Your plant’s health is improving. (Well, at least we hope so!) What happened? Seriously, how much sunlight do plants need?

“Watts” the Big Deal About Sunlight?

Often, we underestimate how much sunlight our plants need. They can struggle through life with improper soil or lack of fertilizer. But what’s the one thing they plant cannot live without? You got it: light. 

Light is crucial to photosynthesis, which creates life-sustaining food for your houseplant. Chloroplasts capture light, causing a metabolic reaction, which results in the creation of carbohydrates that feed your plant. Let’s just say: plants don’t do well on a low-carb diet.

The adaptability of plants never ceases to amaze. They do not have a fixed amount of chloroplast. If a houseplant senses that it is experiencing lower amounts of light, it will produce more chloroplasts to capture as much light as possible (a process called acclimatization). In effect, the plant is making the most of its situation! 

However, that does not mean that plants have an endless supply of chloroplasts and can adapt to life anywhere in your home. (We wish!) This adaptability is just a small cushion that helps your plant cope with the fluctuating light it would receive in nature (due to season changes, etc.). It also explains why some plants “bounce back” by coming to terms with their new environment after hating it.

This fantastic ability makes each of your plants a unique individual. While you still need to research your plant’s species’ required care, you cannot treat any two plants precisely alike. For instance, just because you have a Calathea Rattlesnake that has learned to adapt to a particular location does not mean that a new Rattlesnake plant will do the same.

How Much Sunlight Do Your Plants Need

When answering this question, you must take into consideration the origins of your houseplant. For instance, “understory plants” reside on the forest floor and do not require as much light as a succulent. But is it that simple? Not really.

As soon as you enter your home, the quality of sunlight diminishes drastically. The shadiest corner of the forest floor is likely brighter than the inside of your house. Why? In the outdoors, sunlight floods in from all angles. But indoor light is usually from one primary source (such as a bright window). 

Light and distance have an inverse relationship: as the distance increases, the light decreases. Meaning, your plant could be just a few feet away from your light source (window) and technically be experiencing “low-light” conditions. It lacks that consistent, 365-degree light source that naturally comes outdoors!

How can you tell how much sunlight your plants are getting?

If you’re looking for an easy way to determine how much light your plants are experiencing, check out their shadows when the sun is its brightest. 

  • Bright-light: A stark, finger-puppet-worthy shadow. 
  • Medium-light: Muffled, slight shadows.
  • Low-light: Little to no shadow.

Light duration is also essential. For instance, variegated plants that do not experience a long enough span of bright light will revert to being all-green. If you are supplementing your natural sunlight with grow lights, you can also over-do the duration. Plants have differing daylight cycles (Photoperiodism) and do also require darkness to thrive.

How much sunlight do low-light plants need?

“Low-light” plants will survive in their darker location but will not prosper. Why? As noted, they need brighter light to produce food, supplying them with the energy they need to flourish. Snake plants, for instance, benefit from a growing season outdoors, in the “shade.” After a summer vacation, your Sansevieria will maintain its size through the winter months.

How can you tell if your plants are getting sufficient light?

Plants give us S.O.S. signals when there is something wrong with their care. Below are a few common symptoms that indicate you need to relocate your plant to a brighter location!

  • Paleness. During photosynthesis, plants also produce chlorophyll, which gives them their green pigmentation. If there isn’t enough sun, there isn’t enough chlorophyll.
  • Legginess. We have all heard the term “leggy,” but what does it mean? The stems grow thin and elongated, leaving more space between nodes.

  • A lack of sunlight is not the only issue when it comes to caring for your plants. They also let you know when you are overdoing it.

    Symptoms of overexposure to the sun include:


    • Bleaching, sunburn, or yellowing.
    • Reaching for the light source.



    Some plants, such as the Calathea, use this to indicate that they are receiving too much light. This is not true for every variety of plant, however (such as the Pilea Peperomias). Make sure to research your plant’s species! 


    Making Adjustments

    How much should you change in your plant’s environment to give them their needed sunlight? Make changes slowly and one-at-a-time. Do not expect to see changes overnight. It takes an average of five days for a plant to acclimate to new lighting conditions. Wait to see how your plant responds to its new location rather than quickly relocating it again. Remember, in nature, plants do not uproot and move to a sunnier or shadier spot; they’re stuck where they are. So, be patient with them.

    Do not be surprised if your plant experiences some leaf drop. As long as it continues growing new leaves, it is a sign that your plant is getting used to its new location.

    Don’t Forget to Change Your Watering Habits

    Plants that receive less light require less frequent waterings. The opposite is also true: plants that get more sunlight require more frequent waterings. Monitor your plant’s moisture levels carefully, and only water when they have the appropriate soil-dryness for their species.

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