How Does Light Affect Plant Growth?

Most of us take light for granted, perhaps due to the fact that it is readily available and we only need it so that we can see clearly. Plants, on the other hand, need light to make food, with only an exemption of a few species like mushrooms and algae. The three basic human needs are food air and shelter. For plants, it's light, water, and air. This brings us to the question of the day, how does light affect plant growth?


If there is a topic that is taught adversely in science classrooms is photosynthesis. Back in where I schooled there was a whole unit on photosynthesis. As you advance more details are taught about photosynthesis and we can all understand why. We need plants more than they need us.

What is photosynthesis? Photosynthesis is the ability of plants to make their own food. The food that animals depend on! Plant growth is affected by light in the sense that for photosynthesis to occur light must be present. Without light, plants can’t make food and this explains why the leaves turn yellow once deprived light. What is the green coloring matter in plants? Chlorophyll! This green coloring matter is what is responsible for absorbing light pigments helping the plants carry out photosynthesis.

1. How does light affect plant growth when it comes to photosynthesis?

Now that we have refreshed our memories on what photosynthesis is, it’s high time we understand the whole process and what exactly is the role of light. To begin with, let’s recall a simple fact, plants are autotrophs. In simpler terms plants are capable of making their own nutrients but how do they go about it?

Plants absorb minerals and nutrients from the soil; take in water through the roots and carbon dioxide through the stomata to make food. The three are not complete without light which is the main source of energy. Most plants are grown on the open and for them, the main source of energy is the sun. Recently, more people have embarked on indoor gardening and, though it’s very hard to beat the sun as the source of light, technology has made it possible for the creation of growing bulbs that provide the exact light specifications needed by plants on different growth stages.

Plants need water, carbon dioxide in the presence of chlorophyll and sunlight to oxygen molecules and glucose. The glucose made is used by the plants to enhance growth whereas the oxygen molecules are released by the plants as a by-product. Hence the saying that trees and plants, in general, purify the air. Plants take in the carbon dioxide we breath out and release oxygen during photosynthesis. This only happens when plants are exposed to light, at night plants take in oxygen and release carbon dioxide as we do.

Most likely most of us had forgotten this about photosynthesis but as of now, I am certainly sure that we are all on the same page.

2. Light is essential for direct growth

Have you ever wondered why most plants always have their stems grow straight upright? The few plants whose stem doesn’t grow upright have a week stem and are parasitic plants. They depend on other plans for support and even then they only grow facing upwards. What is the reason behind such behavior or is it all just but a coincidence?

It’s no coincidence, plant always grows towards the light. When exposed to light, auxins hormone is produced on the stems stimulation it to grow towards the light. If you would deprive a plant direct light the stems will bend in almost just any direction in search of light. Plants need light for direct growth; otherwise, the stems would get weak. If you were keen in science classrooms you should recall that the stem is actually the passage of foods from the roots to the leaves. There is an elaborate and defined transport system not visible to the naked eye in the stem of a plant. If the stem would be weak, this means that less food and water would be transported. What happens when you don’t get enough food? You get week and thin. The same thing applies to plants. When the stem is weak and less food is transported to &fro the roots and leaves the plant will get weak and this will affect its growth. All due to lack of direct light!

Different plants store their food differently. There are those that store their food on the leaves, other in the roots whereas other store food in the stems. For the storage process to be effective there must be light especially where the storage is in the stems. Examples of plants that store food in the stems are sugarcane and cactus.

Why do sunflowers face different directions at different times of the day? Most presume it as just normal but if you would ling you would realize that they follow a pattern. And in basic mathematics, a pattern is not a coincidence. In the morning every sunflower faces the east, at not the sunflower it’s upright and in the evening it faces the west. Any, lucky guesses as to what could be causing this? If you guessed light, you are correct if you guessed sunlight, in particular, you need an award.

3. Seasonal effects

Some plants are naturally seasonal. They rely on seasons to either to flower, seed or fertilize. In most countries with 4 seasons, plants blossom during spring and summer. This is the time when the plant's flower and bear fruits. In other seasons with inadequate sunlight, most plants are dormant and their sole purpose is to conserve energy. Some plants every shed off their leaves and appear dry only to rejuvenate back to life later on spring.

How artificial lights are as effective as sunlight?

More and more people are engaging in indoor for farming and this is where one understands the essence of light. Quite frankly, it is not an issue of debate on whether there can be any source of light greater than the sun. The sun is on its own level but technology has enabled us to create grow lights that provide plants with the exact light specifications they need on different stages of growth. We can now change our question from who does light affect plant growth to how effective is artificial light compared to sunlight?

In a grow tent, you need an artificial grow light and there are thousands of brands to choose from. Different grow lights have different features. Some are effective whereas others are not. When it comes to lighting for plant growth the best type of bulbs is none other the LED.

Different light aspects that affect plant growth

led grow lights


More intense light means that there will be more photosynthesis. And, with more photosynthesis plants will grow more. In a grow tent, the intensity of light can be adjusted through reducing or increasing the distance to the plants. The problem with this is that some grow lights emit heat that can harmful to the plants. However, this is not the case with all; some brands have an effective cooling system to ensure little to no heat is emitted.


The longer the duration that plants are exposed to light the higher the rate of growth. With the sun you can’t increase sunlight hour but with grow lights, you can and this is the main reason why indoor gardening yields more returns.

Light spectrum

Light is more of a form of a form of energy that moves in form of electromagnetic waves. Basically, a full light spectrum has 12 bands of different lights. All these lights spectrums are essential for plants growth but the red, blue and violet spectrums are needed in high amount.

  • The red light spectrum

This spectrum is the longest of all but lacks energy. It penetrated dense canopies and evens slights heat the ground. This is the light that supports flowering and blooming in plants. Failure to getting enough of the red light makes plants have delayed flowering.

  • The blue and violet light

These are rather short light waves but high in energy. The blue spectrum light is essential on the vegetative phase of growth. Plants exposed too little or no blue light most likely will turn yellow. This is due to the simple fact that in the presence of magnesium, the blue light helps in the formation of chlorophyll.


Answering the question as whether grow light can be effective as sunlight the answer is a big, yes. It is easy to control lighting to meet plants needs in a grow tent. On the other hand, you can’t control the sun. Most grow lights have switch buttons to control light during vegetative phase and flowering. It is my hope that you found this article on how does light affect plant growth informative and useful. Take a few seconds and share it with a friend or two and don’t forget to leave a comment in the comment section below.

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